Suspended media membrane biological reactor system and process including suspension system

ABSTRACT

A wastewater treatment system is provided comprising a biological reactor having a separation subsystem, a suspension system and a membrane operating system. The separation subsystem is constructed and arranged to maintain adsorbent material in the biological reactor with a mixed liquor. The suspension system is positioned in the biological reactor and is constructed and arranged to maintain adsorbent material in suspension with mixed liquor. The membrane operating system is located downstream of the biological reactor and is constructed and arranged to receive treated mixed liquor from the biological reactor and discharge a membrane permeate.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/224,000 filed Jul. 8, 2009, and U.S. ProvisionalPatent Application No. 61/186,983 filed on Jun. 15, 2009, thedisclosures of which are hereby incorporated by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to wastewater treatment systems and methods.

2. Description of Related Art

Effective handling of domestic sewage and industrial wastewater is anextremely important aspect of increasing the quality of life andconservation of clean water. The problems associated with simplydischarging wastewater in water sources such as rivers, lakes andoceans, the standard practice up until about a half century ago, areapparent—the biological and chemical wastes create hazards to all lifeforms including the spread of infectious diseases and exposure tocarcinogenic chemicals. Therefore, wastewater treatment processes haveevolved into systems ranging from the ubiquitous municipal wastewatertreatment facilities, where sanitary wastewater from domesticpopulations is cleaned, to specialized industrial wastewater treatmentprocesses, where specific pollutants in wastewater from variousindustrial applications must be addressed.

Biologically refractory and biologically inhibitory organic andinorganic compounds are present in certain industrial and sanitarywastewater streams to be treated. Various attempts have been made toaddress treatment of such biologically refractory and biologicallyinhibitory compounds. Certain types of known treatment include use ofpowdered activated carbon to adsorb and subsequently remove biologicallyrefractory and biologically inhibitory organic compounds.

Nonetheless, a need exists to treat wastewater containing biologicallyrefractory and biologically inhibitory organic and inorganic compoundswithout disadvantages associated with using powdered activated carbonand other existing technologies.

SUMMARY OF THE INVENTION

In accordance with one or more embodiments, the invention relates to asystem and method of treating wastewater.

In accordance with one or more embodiments, the invention relates to awastewater treatment system comprising a biological reactor having aseparation subsystem, a suspension system and a membrane operatingsystem. The separation subsystem is constructed and arranged to maintainadsorbent material in the biological reactor with a mixed liquor. Thesuspension system is positioned in the biological reactor and isconstructed and arranged to maintain adsorbent material in suspensionwith mixed liquor. The membrane operating system is located downstreamof the biological reactor and is constructed and arranged to receivetreated mixed liquor from the biological reactor and discharge amembrane permeate.

In accordance with one or more embodiments, the suspension systemcomprises a gas lift suspension system. The gas lift suspension systemcan include at least one draft tube positioned in the biological reactorand a gas conduit having one or more apertures positioned anddimensioned to direct gas to an inlet end of the draft tube. The gaslift suspension system can alternatively include at least one drafttrough positioned in the biological reactor and a gas conduit having oneor more apertures positioned and dimensioned to direct gas to a lowerportion of the draft trough.

In accordance with one or more embodiments, the suspension systemcomprises a jet suspension system.

In accordance with one or more embodiments, the separation subsystemincludes a screen positioned at an outlet of the biological reactor.

In accordance with one or more embodiments, the separation subsystemincludes a settling zone located proximate the outlet of the biologicalreactor. The settling zone can include a first baffle and a secondbaffle positioned and dimensioned to define a quiescent zone in whichthe adsorbent material separates from mixed liquor and settles into themixed liquor in a lower portion of the biological reactor. Further, thesettling zone can include a screen or a weir positioned proximate theoutlet of the biological reactor.

In accordance with one or more embodiments, the invention relates to awastewater treatment system in which a source of adsorbent materialintroduction apparatus in communication with the biological reactor. Inaddition, a sensor is constructed and arranged to measure a parameter ofthe system. Further, a controller is in electronic communication withthe sensor and programmed to instruct performance of an act based on themeasured parameter of the system. The measured parameter can be theconcentration of one or more predetermined compounds. The act caninclude removing at least a portion of the adsorbent material from thebiological reactor, and/or adding adsorbent material to the biologicalreactor.

In accordance with one or more embodiments, the invention relates to awastewater treatment system for treating wastewater. The system includesa biological reactor with a wastewater inlet, a mixed liquor outlet, anda separation subsystem associated with the mixed liquor outlet. Thesystem also includes a suspension system for adsorbent materialpositioned in the biological reactor, and a membrane operating systemlocated downstream of the biological reactor having an inlet in fluidcommunication with the mixed liquor outlet, and a treated effluentoutlet.

In accordance with one or more embodiments, the invention relates to aprocess for treating wastewater. The process includes introducing mixedliquor into a biological reactor; introducing adsorbent material intothe biological reactor with the mixed liquor; suspending the adsorbentmaterial in the mixed liquor using a gas, under operating conditionsthat promote adsorption of contaminants from the mixed liquor by theadsorbent material; and passing an effluent that is substantially freeof adsorbent material from the biological reactor to a membraneoperating system while maintaining adsorbent material in the biologicalreactor.

Still other aspects, embodiments, and advantages of these exemplaryaspects and embodiments, are discussed in detail below. Moreover, it isto be understood that both the foregoing information and the followingdetailed description are merely illustrative examples of various aspectsand embodiments, and are intended to provide an overview or frameworkfor understanding the nature and character of the claimed aspects andembodiments. The accompanying drawings are included to provideillustration and a further understanding of the various aspects andembodiments, and are incorporated in and constitute a part of thisspecification. The drawings, together with the remainder of thespecification, serve to explain principles and operations of thedescribed and claimed aspects and embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail below and withreference to the attached drawings all of which describe or relate toapparatus, systems and methods of the present invention. In the figures,which are not intended to be drawn to scale, each similar component thatis illustrated in various figures is represented by a like numeral. Inthe figures:

FIG. 1 is a schematic diagram of a membrane biological reactor systemusing a biological reactor which contains one or more zones withadsorbent material in suspension;

FIG. 2 is a schematic diagram of an embodiment of a system for treatmentof wastewater using adsorbent material in a biological reactor upstreamof a membrane operating system;

FIG. 3 is a schematic diagram of a second embodiment of a system similarto that shown in FIG. 2 which includes a denitrification zone;

FIG. 4 is a schematic diagram of another embodiment in which adsorbentmaterial is maintained in suspension in only a portion of a biologicalreactor tank;

FIG. 5 is a schematic diagram of a further embodiment of a biologicalreactor divided into multiple sections that includes an anoxic zone;

FIG. 6 is a schematic diagram of an additional embodiment using a seriesof biological reactors in which adsorbent material is maintained insuspension in only one of the biological reactors;

FIG. 7 and FIG. 8 are embodiments of biological reactor systemsdepicting a jet suspension system for suspension of adsorbent materialin mixed liquor;

FIGS. 9 and 10 are alternative embodiments of biological reactor systemsdepicting a jet suspension system for suspension of adsorbent materialin mixed liquor, in which mixed liquor taken from a source that has hadadsorbent material removed;

FIG. 11 is an alternative embodiment depicting a jet suspension systemfor suspension of adsorbent material in mixed liquor in which adsorbentmaterial is not circulated through the jet nozzle;

FIG. 12 is a further embodiment of a biological reactor depicting a gaslift suspension system to provide circulation to maintain adsorbentmaterial in suspension;

FIGS. 13A and 13B are further embodiments depicting a settling zone;

FIG. 14 is a chart depicting feed COD concentration (in milligrams perliter), and the remaining effluent COD concentrations (as percentages ofthe original), at various stages of biological acclimation in a membranebiological reactor system;

FIG. 15 is a schematic illustration of an embodiment of a jet nozzle ofthe type used in an example demonstrating use of a jet suspensionsystem;

FIG. 16 is a schematic illustration of an system configuration used inanother example herein;

FIG. 17 is a chart depicting suspension of adsorbent material undercertain nozzle throat velocities and liquid flow rates as determinedunder various test conditions using the system configuration of FIG. 16;

FIGS. 18 and 19 depict top and sectional views of embodiments ofbiological reactors employed in the system configuration of FIG. 16;

FIG. 20 is a chart depicting attrition as a function of run time forvarious types of adsorbent material in another example herein using agas lift suspension system;

FIG. 21 depicts a top and a sectional view of an embodiment of abiological reactor using a gas lift suspension system;

FIG. 22 is a schematic illustration of flow patterns using the gas liftsuspension system of FIG. 21;

FIG. 23 depicts a top and a sectional view of an embodiment of abiological reactor using another configuration of a gas lift suspensionsystems; and

FIGS. 24 and 25 depict top, side sectional and end sectional views ofembodiments of biological reactors using various configurations of gaslift suspension systems.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, “biologically refractory compounds” refer to those typesof chemical oxygen demand (“COD”) compounds (organic and/or inorganic)in wastewater that are difficult to biologically break down whencontacted with micro-organisms. The “biologically refractory compounds”can have varying degrees of refractory, ranging from those that aremildly refractory to those that are highly refractory.

“Biologically inhibitory compounds” refer to those compounds (organicand/or inorganic) in wastewater that inhibit the biologicaldecomposition process.

“Biologically labile” means easy-to-digest, simple organics such ashuman and animal waste, food waste, and inorganics, such as ammonia andphosphorous-based compounds.

“COD” or “Chemical Oxygen Demand,” refers to a measure of the capacityof water to consume oxygen during a chemical reaction that results inthe oxidation (decomposition) of organic matter and the oxidation ofinorganic chemicals such as ammonia and nitrite. COD measurementincludes biologically labile, biologically inhibitory and biologicallyrefractory compounds.

“Mixed liquor suspended solids,” or “MLSS,” means microbes and othersubstances, both dissolved and suspended, present in wastewater beingtreated; “mixed liquor volatile suspended solids,” or “MLVSS,” means theactive microbes in the MLSS; and “mixed liquor” means the combinedmixture of wastewater and MLSS.

“Adsorbent” or “adsorbent materials” as used herein means one or more ofgranular activated carbon, including granular activated carbon that hasbeen treated to provide affinity to predetermined chemical species,metals or other compounds found to be present in the wastewater that isto be treated; granular iron-based compounds, e.g., iron oxidecomposites; synthetic resins; and granular alumino-silicate composites.

“Substantially free” or “substantially prevented” in the context ofdescribing the presence of adsorbent material in effluent passing fromone section of a system to another, e.g., from a biological reactorcontaining suspended adsorbent material to a membrane operating system,refers to limiting the amount of adsorbent material passing to themembrane operating system to an amount that does not adversely effectthe requisite efficacy of the membrane filtration process therein. Forinstance, in certain embodiments, “substantially free” or “substantiallyprevented” refers to retaining at least about 80% by volume of thepredetermined amount of adsorbent material to be used in a given systemwithin the biological reactor or one or more biological reaction zones,in further embodiments, at least about 90% by volume and in stillfurther embodiments at least about 95% by volume, and in yet stillfurther embodiments at least about 99% by volume. However, it will beappreciated by one of ordinary skill in the art based upon the teachingsherein that these percentages are merely illustrative, and can varydepending on factors including but not limited to the type ofmembrane(s) used and their resistance to abrasion, the requisiteeffluent quality, the predetermined amount of adsorbent material to beused in a given system, and other factors.

This invention in directed to wastewater treatment systems and methods.“Wastewater” as used herein, defines any water to be treated such assurface water, ground water, and a stream of wastewater from industrial,agricultural and municipal sources, having pollutants of biodegradablematerial, inorganic, labile organic compounds capable of beingdecomposed by bacteria, biologically refractory compounds, and/orbiologically inhibitory compounds, flowing into the wastewater treatmentsystem.

Wastewater from industrial and municipal sources typically containsbiological solids, and inert material and organics, includingbiologically inhibitory and refractory organics. Examples ofbiologically inhibitory and refractory organics may include syntheticorganic chemicals, such as polyelectrolyte treatment chemicals. Otherbiologically inhibitory and refractory organics include polychlorinatedbiphenyls, polycyclic aromatic hydrocarbons, polychlorinateddibenzo-p-dioxin, and polychlorinated dibenzofurans. Endocrinedisrupting compounds are also a class of biologically inhibitory andrefractory organics which can affect hormone systems in organisms andare found in the environment. Examples of endocrine disrupting compoundsinclude: alkylphenolics, such as nonylphenol used for removing oil aswell as natural hormones and synthetic steroids found in contraceptives,such as 17-b-estradiol, estrone, testosterone, ethynyl estradiol.

Other examples of wastewaters to be treated include: high strengthwastewater; low strength wastewater; and leachate from landfills. Watersmay also be treated to remove viruses. Other examples of pollutants inwastewater include: flame retardants, solvents, stabilizers,polychlorinated biphenyls (PCBs); dioxins; furans; polynuclear aromaticcompounds (PNAs); pharmaceuticals, petroleum; petrochemical products;petrochemical byproducts; cellulose; phosphorous; phosphorous compoundsand derivatives; and agricultural chemicals such as those derived fromor used to produce fertilizers, pesticides, and herbicides.

Wastewater from industrial and municipal sources may also contain traceconstituent compounds that originate during the water treatment processand are subsequently difficult to remove. Examples of trace constituentsintroduced during the water treatment process include nitrosamines, suchas N-nitrosodimethylamine (NDMA) which may be released from proprietarycationic and anionic resins.

In general, wastewater treatment facilities use multiple treatmentstages to clean water so that it may be safely released into bodies ofwater such as lakes, rivers, and streams. Presently, many sanitarysewage treatment plants include a preliminary treatment phase in whichmechanical means are used to remove large objects (e.g., bar screens),and a sand or grit channel where sand, grit and stones settle. Sometreatment systems also include a primary stage where certain fats,greases and oils float to the surface for skimming, and heavier solidssettle to the bottom, and are subsequently treated in an aerobic oranaerobic digester to digest biomass and reduce the levels of biologicalsolids.

After preliminary and/or primary treatment, the wastewater is then sentto a secondary biological activated sludge treatment phase. Biologicaltreatment of wastewater is widely practiced. Wastewater is commonlytreated with waste activated sludge, in which biological solids areacted upon by bacteria within a treatment tank. Activated sludgeprocesses involve aerobic biological treatment in an aeration tank,typically followed by a clarifier/settling tank. Settled sludge isrecycled back to the aeration tank in order to maintain an adequatemixed liquor suspended solids concentration to digest the contaminants.Some alternatives available for disposal of excess bio-solids, e.g.,sludge, include but are not limited to incineration, disposal in alandfill, or use as fertilizer if there are no toxic components.

In the aeration tank, an oxygen-containing gas such as air or pureoxygen is added to the mixed liquor. The oxygen from the air istypically used by the bacteria to biologically oxidize the organiccompounds that are either dissolved or carried in suspension within thewastewater feed. Biological oxidation is typically the lowest costoxidation method available to remove organic pollutants and someinorganic compounds, such as ammonia and phosphorous compounds, fromwastewater and is the most widely used treatment system for wastewatercontaminated with biologically treatable organic compounds. Wastewatersthat contain compounds entirely resistant to bio-decomposition,biologically inhibitory compounds, and/or biologically refractorycompounds may not be treated adequately by a conventional simplebiological wastewater treatment system. These compounds can only beacted upon by the bacteria only during a hydraulic retention time withina treatment tank. Because the hydraulic retention time is generallyinsufficient for biological oxidation of sufficient biologicallyinhibitory compounds and/or biologically refractory compounds, it islikely that some of these recalcitrant compounds may not be treated ordestroyed and can pass through a treatment process unchanged or onlypartially treated prior to discharge in either an effluent or excessresidual sludge.

The mixed liquor effluent from the aeration tank typically enters aclarifier/settling tank where sludge, including concentrated mixedliquor suspended solids, settles by gravity. Excess biomass is wasted,i.e., discharged, to off-site disposal. However, based on the wastewaterand economic needs, some biological oxidation systems use a differenttreatment method to remove the solids from the wastewater effluent. Theclarifier/settling tank can be replaced with a membrane operatingsystem, or another unit operation such as a dissolved/induced airflotation device can be used. The liquid effluent from theclarifier/settling tank, operating system or dissolved air flotationdevice is either discharged or given further treatment prior todischarge. The solids that are removed from the mixed liquor arereturned to the aeration tank as return activated sludge for furthertreatment and in order to retain an adequate concentration of bacteriain the system. Some portion of this return activated sludge isperiodically removed from this recycle line in order to control theconcentration of bacteria in the mixed liquor.

One recent advance in conventional industrial biological wastewatertreatment plant technology includes the addition of powdered activatedcarbon particles to the mixed liquor. In biological treatment processesutilizing powdered activated carbon, the organics can be adsorbed ontothe activated carbon and remain within the treatment tank for ahydraulic retention time that is similar to the sludge residence timeand therefore undergo both adsorptive and biological treatments thatresult in enhanced removal of certain biologically inhibitory orrefractory compounds. In these processes, certain organic and inorganiccompounds are physically adsorbed to the surface of the powderedactivated carbon particles.

Powdered activated carbon has been used in conventional biologicaltreatment plants because of its ability to adsorb biologicallyinhibitory and biologically refractory compounds, thereby providing aneffluent with lower concentrations of these pollutants. Inclusion ofpowdered activated carbon in the mixed liquor provides a number ofoperational benefits. The carbon provides the advantages of a suspendedmedia biological treatment system which include increased pollutantremoval and increased tolerance to upset conditions. Additionally, thecarbon allows the biologically inhibitory and biologically refractorycompounds to adsorb onto the surface of the carbon and to be exposed tothe biology for a significantly longer period of time than in aconventional biological treatment system, thereby providing benefitssimilar to that of a fixed film system. The carbon also allows for theevolution of specific strains of bacteria that are more capable ofdigesting the biologically inhibitory organic materials. The fact thatthe carbon is continuously recycled back to the aeration tank with thereturn activated sludge, i.e., the sludge residence time, means that thebacteria can work on digesting the biologically inhibitory organiccompounds adsorbed onto the surface of the carbon for a period of timelonger than the hydraulic detention time of the biological treatmentsystem. This process also results in biological regeneration of thecarbon and allows the carbon to remove significantly more biologicallyinhibitory and biologically refractory compounds than it could in asimple packed bed carbon filter system which would also require frequentreplacement or costly physical regeneration of the carbon once theadsorption capacity of the carbon is exhausted. The carbon in the mixedliquor can also adsorb certain compounds and therefore provide aneffluent that is free of or hasw a substantially reduced concentrationof compounds that are not treatable by conventional biological oxidationor otherwise entirely resistant to bio-decomposition. One example of aknown powder activated carbon system is offered by Siemens WaterTechnologies under the trademark “PACT®.”

However, because both biological growth and adsorption of organic andinorganic compounds occurs on the activated carbon in powder form,wasting of excess solids is required. In addition, the powderedactivated carbon is discharged from the treatment process with theremoval of biosolids and must, therefore, be continually replaced.

Increasingly, sanitary wastewater is being treated using membranebiological reactor technology, which offers improved effluent quality, asmaller physical footprint (more wastewater can be treated per unitarea), increased tolerance to upsets, improved ability to processhard-to-treat wastewaters and a variety of other operational advantages.For example, wastewaters containing high total dissolved solids canexperience settling problems in a conventional clarifier/settling tankand requires significantly more difficult-to-operate solids separationdevices such as a dissolved air flotation device or some other solidsremoval system. However, while membrane biological reactors eliminatethe settling problems experienced with clarifier/settling tank systems,they often present problems of membrane fouling and foaming that do notoccur in conventional systems using clarifiers. Membrane fouling may bethe result of extra-cellular polymeric compounds that result from thebreak-down of the biological life forms in the mixed liquor suspendedsolids, accumulation of organic materials such as oils, or by scaling byinorganic materials.

In addition, to date, membrane biological reactors have not beenutilized commercially with powdered activated carbon addition. There hasbeen some use of powdered activated carbon in surface water treatmentsystems that utilize membranes for filtration. However, it has beenreported that these surface water treatment systems using membranes andpowdered activated carbon have problems with the carbon abrading themembranes and the carbon permanently plugging and/or fouling themembranes.

Industrial wastewater that must be treated prior to discharge or reuseoften include oily wastewaters, which can contain emulsifiedhydrocarbons. Oily wastewaters can come from a variety of industriesincluding steel and aluminum industries, chemical processing industries,automotive industries, laundry industries, and crude oil production andpetroleum refining industries. As discussed above, a certain amount ofnon-emulsified oils and other hydrocarbons may be removed in primarytreatment processes, where floating oils are skimmed from the top.However, biological secondary wastewater processes are generallyemployed to remove the remaining oils from wastewater, typically thedissolved and emulsified oils, though some free oil may exist. Typicalhydrocarbons remaining after primary treatment can include lubricants,cutting fluids, tars, grease, crude oils, diesel oils, gasoline,kerosene, jet fuel, and the like. These hydrocarbons typically must beremoved prior to discharge of the water into the environment or reuse ofthe water in the industrial process. In addition to governmentalregulations and ecological concerns, efficient removal of the remaininghydrocarbons also has benefits, as adequately treated wastewater may beused in many industrial processes and eliminate raw water treatmentcosts and reduce regulatory discharge concerns.

Other types of wastewater that must be treated includes contaminatedprocess water from other industrial processes such as manufacturing ofpharmaceuticals, various goods, agricultural products (e.g.,fertilizers, pesticides, herbicides), and paper processing, as well asmedical wastewater.

Commercial deployment of membrane biological reactors in the treatmentof oily/industrial wastewater has been very slow to develop, mainly dueto maintenance problems associated with oil and chemical fouling of themembranes. Testing of industrial/oily wastewater treated in a membranebiological reactor having powdered activated carbon added to the mixedliquor indicated the same treatment advantages as observed inconventional biological wastewater treatment systems including powderedactivated carbon. It was also noted that the advantages of using amembrane biological reactor can also achieved. However, a side-by-sidecomparison of membrane biological reactors with and without the additionof powdered activated carbon demonstrated that the membrane biologicalreactor with powdered activated carbon provided treatment advantages ascompared to the membrane biological reactors without activated carbon.Additionally, the membrane biological reactor without the carbonaddition was very difficult to operate because of dissolved organics andextra cellular polymeric compounds fouling the membranes. Testingfurther demonstrated that while the addition of powdered activatedcarbon provided a very viable biological wastewater treatment system,the carbon had the deleterious effect of a significant amount ofabrasion to and non-reversible fouling of the membranes. This abrasionand non-reversible fouling was significant enough to result in thissystem being very costly to operate, because of the significantlydecreased life expectancy of the membranes and membrane cleaningfrequency.

The systems and methods of the present invention overcome thedeleterious effects of using powdered activated carbon, while providingthe same and additional advantages.

Referring to FIG. 1, a wastewater treatment system 100 is schematicallydepicted including a biological reactor system 102 upstream of amembrane operating system 104. In certain embodiments, biologicalreactor system 102 includes a single biological reactor vessel. Inadditional embodiments, biological reactor system 102 includes aplurality of biological reactor vessels, one biological reactor vesseldivided into separate sections, or a plurality of biological reactorvessels some or all of which can be divided into separate sections. Theindividual reactor vessels or segregated sections are generally referredto herein as biological reaction zones. During wastewater treatmentoperations according to the present invention, adsorbent material alongwith micro-organisms are maintained in suspension in all of thebiological reaction zones or a subset of the total number of biologicalreaction zones. The membrane operating system 104 is maintainedsubstantially free of adsorbent material using one or more of theseparation subsystems described herein. An influent wastewater stream106 can be introduced from a primary treatment system, a preliminaryscreening system, or as a direct flow of previously untreatedwastewater. In further embodiments, the influent wastewater stream 106can be previously treated wastewater, e.g., an effluent from one or moreupstream biological reactors, including but not limited to aerobicbiological reactors, anoxic biological reactors, continuous flowreactors, sequencing batch reactors, or any number of other types ofbiological treatment systems capable of biologically degrading organicand in certain embodiments some inorganic compounds.

The biological reactor(s) and/or certain biological reactor zones can bevarious types of biological reactors, including but not limited toaerobic biological reactors, anoxic biological reactors, continuous flowreactors, sequencing batch reactors, trickling filters, or any number ofother types of biological treatment systems capable of biologicallydegrading organic and in certain embodiments some inorganic compounds.

In addition, the biological reactor(s) and/or certain biological reactorzones used herein can be of any size or shape suitable to suspendadsorbent material in conjunction with the suspension system. Forexample, the vessel may have a cross sectional area of any shape, suchas circular, elliptical, square, rectangle, or any irregular shape. Insome embodiments, the vessel may be constructed or modified in order topromote suitable suspension of the adsorbent material.

FIG. 2 schematically depicts the process flow of a wastewater treatmentsystem 200 for producing a treated effluent having reducedconcentrations of biologically labile, biologically refractory,biologically inhibitory and/or organic and inorganic compounds that areentirely resistant to biological decomposition. System 200 generallyincludes a biological reactor 202 and a membrane operating system 204.Biological reactor 202 includes an inlet 206 for receiving wastewaterand an outlet 208 for discharging effluent that has been biologicallytreated, including mixed liquor volatile suspended solids and/or mixedliquor, to the membrane operating system 204.

The biological reactor 202 includes a distributed mass of porous 236adsorbent material 234, and an effective amount of one or moremicro-organisms 238, that are both adhered to the adsorbent material andfree-floating and separate from the adsorbent material in the mixedliquor, for acting on biologically labile and certain biologicallyrefractory and/or biologically inhibitory compounds in the mixed liquor.The adsorbent material adsorption sites, including the outer surface ofthe adsorbent granules or particles, and the wall surfaces of pores 236,initially serve as adsorption sites for the biologically labile,biologically refractory, biologically inhibitory and/or organic andinorganic compounds that are entirely resistant to biologicaldecomposition. In addition, micro-organisms 238 can be adsorbed on theadsorption sites of the adsorbent material. This allows for higherdigestion levels of certain biologically refractory and/or biologicallyinhibitory compounds without requiring proportionally longer hydraulicretention times and sludge retention times, due to the fact thosecertain biologically refractory and/or biologically inhibitory compoundsare retained for extended periods of time on the adsorbent material,which are isolated or retained in the biological reactors.

Generally, biologically labile compounds and certain inorganics will bedigested relatively quickly and predominantly by the micro-organismsthat are not adhered to the adsorbent material, i.e., the free floatingmicro-organisms in the mixed liquor. Certain components includingorganics and inorganics that are entirely resistant to biologicaldecomposition and very refractory biologically refractory andbiologically inhibitory compounds will remain adsorbed on the adsorbentmaterial or may be adsorbed and/or absorbed by free-floating biologicalmaterial in the reactor(s). Ultimately, these non-digestible compoundswill concentrate on the adsorbent to the point where the replacement ofthe adsorbent will be required to maintain the effluent at an acceptablelevel of adsorptive capacity. As the adsorbent material remains in thesystem according to the present invention, micro-organisms grow and areretained on the adsorbent material, generally long enough to break downat least certain biologically refractory and/or biologically inhibitorycompounds in the particular influent wastewater, which have beenconcentrated on the adsorbent material. In addition, while not wishingto be bound by theory, it is believed that micro-organisms caneventually evolve into mature strains with specific acclimationnecessary to break down the hard-to-treat compounds in the particularinfluent wastewater. Over additional time, e.g., several days to severalweeks, in which adsorbent material having certain biologicallyrefractory and/or biologically inhibitory compounds is maintained in thesystem, the micro-organisms having a high degree of specificity becomesecond, third, and higher generations, thereby increasing their efficacyto biodegrade at least certain of the specific biologically refractoryand/or biologically inhibitory compounds that are present in theparticular influent wastewater as the system becomes acclimated. This isdepicted by the step change in residual COD depicted in FIG. 14, whichshows a plot of feed concentration (in milligrams per liter) ofbiologically refractory and biologically inhibitory compounds, and theremaining effluent concentrations (as percentages of the original), atvarious stages of the acclimation of a membrane biological reactorsystem with adsorbent material added, i.e., stage A that is beforeadsorbent material is added, stage B that is during the acclimationperiod, and stage C that is after acclimation.

Various influent wastewaters can be deficient in certain nutrientsbeneficial to the biology that occurs in the biological reactor 202.Further, certain influent wastewaters can have pH levels that areexcessively acidic or caustic. Accordingly, as will be apparent to aperson having ordinary skill in the art, phosphorus, nitrogen, and pHadjustment materials or chemicals can be added to maintain optimalnutrient ratios and pH levels for the biological life and associatedactivity, including biological oxidation, in the reactor 202.

Effluent from the biological reactor 202 is introduced via a separationsubsystem 222 to an inlet 210 of the membrane operating system 204. Thistransferred mixed liquor, having been treated in biological reactor 202,is substantially free of adsorbent material. In the membrane operatingsystem 204, the wastewater passes through one or more microfiltration orultra-filtration membranes, thereby eliminating or minimizing the needfor clarification and/or tertiary filtration. Membrane permeate, i.e.,liquid that passes through the membranes 240, is discharged from themembrane operating system 204 via an outlet 212. Membrane retentate,i.e., solids from the biological reactor 202 effluent, includingactivated sludge, is returned to the biological reactor 202 via a returnactivated sludge line 214.

Spent adsorbent material from the biological reactor 202, e.g., granularactivated carbon that is no longer effective in adsorbing contaminantssuch as certain compounds entirely resistant to bio-decomposition,biologically refractory compounds and biologically inhibitory compounds,can be removed via a mixed liquor waste discharge port 216 of thebiological reactor 202. A waste outlet 218 can also be connected to thereturn pipe 214 to divert some or all the return activated sludge fordisposal, for instance, to control the concentration of the mixed liquorand/or culture. Sludge is discharged from the apparatus with the wasteactivated sludge when it increases to the point where the mixed liquorsolids concentration is so high that it disrupts the operation of theparticular membrane biological reactor system. In addition, the mixedliquor waste discharge port 216 can be used to remove a portion of theadsorbent material, thereby removing some portion of the biologicallyrefractory compounds, biologically inhibitory compounds, and/or organicand inorganic compounds that are entirely resistant to biologicaldecomposition, rather than from the return activated sludge line withthe waste activated sludge, resulting in a lower concentration of thesebiologically refractory compounds, biologically inhibitory compounds,and/or organic and inorganic compounds that are entirely resistant tobiological decomposition in the discharge and a more stable biomass inthe membrane biological reactor. An equivalent quantity of fresh orregenerated adsorbent material can be added.

A preliminary screening and/or separation system 220 can be providedupstream of the inlet 206 of the biological reactor 202. Thispreliminary screening and/or separation system can include a dissolvedair floatation system, a coarse screen or a combination of these and/orother preliminary treatment devices for separating suspended matter ofthe type known in the art. Optionally, the preliminary screening and/orseparation system 220 can be eliminated, or other types of preliminarytreatment devices may be included, depending on the particularwastewater being treated.

In order to prevent at least a majority of the adsorbent material 234from entering the membrane operating system 204 and causing undesirableabrasion and/or fouling of the membranes 240, separation subsystem 222is provided. As shown, in FIG. 2, the separation subsystem 222 islocated proximate the outlet of the biological reactor 202. However, incertain embodiments, the separation subsystem 222 can be positioned in aseparate vessel downstream of the biological reactor 202. In eithercase, the separation subsystem 222 includes suitable apparatus and/orstructures for preventing contact between at least a majority of theadsorbent 234 and the membranes 240 in the membrane operating system204. Separation subsystem 222 can comprise one or more of a screeningapparatus, a settling zone, and/or other suitable separation apparatus.

Suitable types of screens or screening apparatus for use in certainembodiments of the present invention include wedge wire screens, metalor plastic apertured plates, or woven fabrics, in cylindrical or flatconfigurations and arranged at various angles including verticallyoriented, horizontally oriented, or at any angle therebetween. Infurther embodiments, an active screening apparatus can be employed suchas a rotating drum screen, vibrating screen or other moving screeningapparatus. In general, for systems in which the separation subsystem 222is a screening apparatus, the mesh size is smaller than the bottom limitof the effective granule or particle size of the adsorbent material thatis being used.

Other types of separation subsystems can also be used in the separationsubsystem, as alternatives to, or in combination with, a screeningapparatus. For instance, as further described below, a settling zone canbe provided, in which adsorbent material settles by gravity.

In alternative embodiments, or in conjunction with previously describedembodiments, separation subsystems can include a centrifugal system(e.g., hydrocyclone, centrifuge, or the like), an aerated grit chamber,a floatation system (such as induced gas flotation or dissolved gas), orother known apparatus.

Optionally, or in combination with the separation subsystem 222proximate the outlet of biological reactor 202, a separation subsystemcan be provided between biological reactor 202 and the membraneoperating system 204 (not shown). This alternative or an additionalseparation subsystem can be the same as or different as separationsubsystem 222, in type and/or dimension. For instance, in certainembodiments, a settling zone, a clarifier, a hydrocyclone separator, acentrifuge, or a combination of these can be provided as a distinct unitoperation between biological reactor 202 and membrane operating system204.

Note that the separation subsystem 222 is highly effective forpreventing passage of adsorbent material in its original dimension tothe membrane operating system. In certain preferred embodiments, theseparation subsystem 222 prevents substantially all of the adsorbentmaterial 234 from passage to the membrane operating system 204. However,during operation of the system 200, various causes of attrition of theadsorbent material, including inter-granule collisions, shearing,circulation, or collisions of granules within stationary or movingequipment, can cause particles to be created that are too small to beeffectively retained with the separation subsystem 222. In order tominimize the detriment to the membranes and loss of adsorbent materialto wasting, certain embodiments include a separation subsystem 222 thatis capable of preventing passage of substantially all of the adsorbentmaterial 234 within about 70 to about 80 percent of its originaldimension. The acceptable percentage reduction in the original dimensioncan be determined by a person having ordinary skill in the art, forinstance, based on an economic evaluation. If the reduction in thedimension results in an increase in the particles passing through thescreening system, the membranes will experience increased abrasion.Thus, a cost-benefit analysis can be used to determine what is anacceptable percentage reduction of adsorbent material based on the costof abrasion and eventual replacement of the membranes as compared to thecosts associated with adsorbent material that minimizes breakage, andhandling and operational costs associated with a separation subsystemcapable of preventing passage of particles much smaller than theoriginal adsorbent material granules or particles. In addition, incertain embodiments, some degree of inter-granule collisions, orcollisions of granules within stationary or moving equipment, isdesirable to strip excess biomass from the outer surfaces of theadsorbent material.

Screened or separated mixed liquor effluent from the biological reactor202 can be pumped or flow by gravity (depending on the design of theparticular system) into the membrane operating system 204. In a systemusing an external separation subsystem (not shown), the apparatus ispreferably configured such that adsorbent material separated from themixed liquor passing through an external fine screen or separatorsubsystem falls by gravity back into the biological reactor 202.

Adsorbent material such as granular activated carbon, e.g., suitablypre-wetted to form a slurry of adsorbent material, can be added to thewastewater at various points in the system 200, e.g., from a source 229of adsorbent material. As shown in FIG. 2, adsorbent material can beintroduced at one or more locations 230 a, 230 b, 230 c and/or 230 d.For instance, adsorbent material can be added to the feedstreamdownstream of the preliminary screening system 220 (e.g., location 230a). Optionally, or in combination, adsorbent material can be addeddirectly to the biological reactor 202 (i.e., location 230 b). Incertain embodiments, adsorbent material can be introduced via the returnactivated sludge line 214 (e.g., location 230 c). In additionalembodiments, it can be desirable to add the adsorbent material upstreamof the preliminary screening system 220 (e.g., location 230 d), wherethe preliminary screening system 220 is designed specifically for thisapplication by including screening that allows the adsorbent material topass through and into the biological reactor 202. Mixed liquor passesthrough the separation subsystem 222 and the adsorbent material issubstantially prevented from passing into the membrane operating system204 with the mixed liquor suspended solids.

As the adsorbent material remains in the system and is exposed towastewater constituents including biologically refractory, biologicallyinhibitory compounds and/or organic and inorganic compounds that areentirely resistant to biological decomposition, some or all of theadsorbent material will become ineffective for treating theconstituents, i.e., the adsorption capacity decreases. This will resultin a higher concentration of these constituents entering the membraneoperating system 204, where they pass through the membranes, and aredischarged with the membrane effluent 212. In addition, adsorbentmaterial can become ineffective due to coating with bacteria,polysaccharides and/or extracellular polymeric substances. This layer ofcoating can reach levels where it blocks the pore sites and therebyprevents access for biologically refractory, biologically inhibitoryand/or organic and inorganic compounds that are entirely resistant tobiological decomposition, and consequently prevents adsorption andinhibits biodegradation. In certain embodiments of the presentinvention, this coating can be removed by a shearing action produced byone or more mechanisms in the system, such as collisions betweenadsorbent material granules suspended in the mixed liquor or shearingforces associated with suspension and/or movement of the adsorbentmaterial.

When adsorbent material has lost all or a portion of its efficacy forreducing the effluent concentration of biologically refractory,biologically inhibitory and/or organic and inorganic compounds that areentirely resistant to biological decomposition, a portion of theadsorbent material can be wasted via waste port 216, e.g., bydischarging a portion of the mixed liquor containing adsorbent materialdispersed therein.

Additional fresh or regenerated adsorbent material can be introducedinto the system, as described above, via adsorbent material introductionapparatus 229 and/or at one or more suitable addition locations. Theinlet wastewater and the effluent wastewater COD compound concentrationsand/or inorganic compound concentrations, can be monitored to determinewhen the adsorbent material and its accompanying biomass in the systemhave experienced reduced effectiveness. A plot of the difference betweenthe inlet and effluent COD divided by the inlet COD concentration willshow gradual loss of the efficacy of the adsorbent material in the mixedliquor. The same type of plot can be used to monitor the inorganicremoval capacity of the system. The amount of COD removed from the feedstream can provide an indication of the relative amount of biologicallyrefractory and/or biologically inhibitory organic compounds that arebeing removed from the wastewater feed. As the operators of the systemdevelop experience with treating a particular wastewater, they will beable to determine when this ratio indicates a point at which there is aneed to remove a portion of the adsorbent material in the biologicalreactor and replace it with fresh adsorbent material. The system'srequired efficiency will be regained for the compounds that arebiologically refractory, biologically inhibitory and/or entirelyresistant to bio-decomposition, for instance, to produce an effluentthat is in compliance with regulatory requirements. Sampling andanalysis of the effluent for concentrations of specific organic andinorganic compounds can also be used to determine when efficacy of theadsorbent material and its accompanying biomass in the mixed liquor hasbeen reduced and partial replacement should be initiated.

The operator of a membrane biological reactor system 200 according tothe invention can begin replacing some of the adsorbent material whenthe effluent concentrations of specific organic or inorganic compoundsstart to approach the facility's permitted discharge concentrations forthese compounds. The allowed discharge concentrations are typicallylimited by the facility's permit, for instance, as determined by theNational Pollutant Discharge Elimination System (NPDES) permit programthat is regulated by the United States Environmental Protection Agency,or other similar regulating body in a particular state or nation. Asoperators gain experience in operating this system with their particularwastewater, they will be able to anticipate when to commence replacementof adsorbent material. When the operator determines that the efficacy ofthe adsorbent material and its accompanying biomass is approaching aninability to achieve the requisite effluent concentration of pollutants,the normal wasting of excess biomass that is performed by wasting returnactivated sludge from line 218 can cease and the excess biomass and theaccompanying adsorbent material is wasted from the biological reactor202 via waste port 216. The amount of material wasted is determined bywhat is required to maintain the mixed liquor suspended solids withinthe optimum operating range for the particular membrane biologicalreactor system. After replacement of a portion of the adsorbentmaterial, the effluent is monitored by the operator to determine whetherthe requisite contaminant removal efficiency has been restored.Additional replacement can be made as needed based on operatingexperience.

In some embodiments, the system and/or individual apparatus of thesystem can include a controller to monitor and adjust the system asdesired. A controller can direct any of the parameters within the systemdepending upon the desired operating conditions, which may, for example,be based on governmental regulations regarding effluent streams. Thecontroller can adjust or regulate valves, feeders or pumps associatedwith each potential flow based upon one or more signals generated bysensors or timers positioned within the system or individual apparatus.The controller can also adjust or regulate valves, feeders or pumpsassociated with each potential flow based upon one or more signalsgenerated by sensors or timers, which indicate a specific trend, forexample an upward or downward trend in a characteristic or property ofthe system over a predetermined period of time. For example, a sensor inan effluent stream can generate a signal indicating that theconcentration of pollutants such as biologically refractory compounds,biologically inhibitory compounds, and or compounds entirely resistantto bio-decomposition has reached a predetermined value or trend, orindicating that the COD level, thereby triggering the controller toperform some act upstream from, downstream from, or at the sensor. Thisact can include any one or more of removing adsorbent material from thebiological reactor, adding new or regenerated adsorbent material to thebiological reactor, adding a different type of adsorbent material,adjusting flow of the wastewater at the feed inlet or inlet to anotherapparatus within the system, redirecting flow of the feed inlet or inletto another apparatus within the system to a storage tank, adjusting airflow within the biological reactor, adjusting residence time within thebiological reactor or other apparatus, and adjusting temperature and/orpH within the biological reactor or other apparatus. One or more sensorscan be utilized in or with the one or more apparatus or streams of thesystem to provide an indication or characteristic of the state orcondition of any one or more processes being performed in the system.

The system and controller of one or more embodiments of the inventionprovide a versatile unit having multiple modes of operation, which canrespond to multiple inputs to increase the efficiency of the wastewatertreatment system of the present invention. The controller can beimplemented using one or more computer systems which can be, forexample, a general-purpose computer. Alternatively, the computer systemcan include specially-programmed, special-purpose hardware, for example,an application-specific integrated circuit (ASIC) or controllersintended for water treatment systems.

The computer system can include one or more processors typicallyconnected to one or more memory devices, which can comprise, forexample, any one or more of a disk drive memory, a flash memory device,a RAM memory device, or other device for storing data. The memory istypically used for storing programs and data during operation of thesystem. For example, the memory can be used for storing historical datarelating to the parameters over a period of time, as well as operatingdata. Software, including programming code that implements embodimentsof the invention, can be stored on a computer readable and/or writeablenonvolatile recording medium, and then typically copied into memorywherein it can then be executed by one or more processors. Suchprogramming code can be written in any of a plurality of programminglanguages or combinations thereof.

Components of the computer system can be coupled by one or moreinterconnection mechanisms, which can include one or more busses, e.g.,between components that are integrated within a same device, and/or anetwork, e.g., between components that reside on separate discretedevices. The interconnection mechanism typically enables communications,e.g., data, instructions, to be exchanged between components of thesystem.

The computer system can also include one or more input devices, forexample, a keyboard, mouse, trackball, microphone, touch screen, andother man-machine interface devices as well as one or more outputdevices, for example, a printing device, display screen, or speaker. Inaddition, the computer system can contain one or more interfaces thatcan connect the computer system to a communication network, in additionor as an alternative to the network that can be formed by one or more ofthe components of the system.

According to one or more embodiments of the invention, the one or moreinput devices can include sensors for measuring any one or moreparameters of system and/or components thereof. Alternatively, one ormore of the sensors, pumps, or other components of the system, includingmetering valves or volumetric feeders, can be connected to acommunication network that is operatively coupled to the computersystem. Any one or more of the above can be coupled to another computersystem or component to communicate with the computer system over one ormore communication networks. Such a configuration permits any sensor orsignal-generating device to be located at a significant distance fromthe computer system and/or allow any sensor to be located at asignificant distance from any subsystem and/or the controller, whilestill providing data therebetween. Such communication mechanisms can beaffected by utilizing any suitable technique including but not limitedto those utilizing wireless protocols.

Although the computer system is described by way of example as one typeof computer system upon which various aspects of the invention can bepracticed, it should be appreciated that the invention is not limited tobeing implemented in software, or on the computer system as exemplarilyshown. Indeed, rather than implemented on, for example, a generalpurpose computer system, the controller, or components or subsectionsthereof, can alternatively be implemented as a dedicated system or as adedicated programmable logic controller (PLC) or in a distributedcontrol system. Further, it should be appreciated that one or morefeatures or aspects of the invention can be implemented in software,hardware or firmware, or any combination thereof. For example, one ormore segments of an algorithm executable by a controller can beperformed in separate computers, which in turn, can be in communicationthrough one or more networks.

In some embodiments, one or more sensors can be included at locationsthroughout of the system 200, which are in communication with a manualoperator or an automated control system to implement a suitable processmodification in a programmable logic controlled membrane biologicalreactor system. In one embodiment, system 200 includes a controller 205which can be any suitable programmed or dedicated computer system, PLC,or distributed control system. The concentration of certain organicand/or inorganic compounds can be measured at the membrane operatingsystem effluent 212 or the effluent from outlet 208 of the biologicalreactor 202, as indicated by dotted line connections between thecontroller 205 and both the effluent line 212 and the intermediateeffluent line between outlet 208 and inlet 210. In another embodiment,the concentration of volatile organic compounds or other property orcharacteristic of the system may be measured at one or more of inlets201, 206, or 210. Sensors known to those of ordinary skill in the art ofprocess control apparatus can include those based on laser-inducedfluorescence or any other sensor suitable for in situ real timemonitoring of the concentration of organic or inorganic compounds in theeffluent or other property or characteristic of the system. Sensors thatmay be used include submersible sensors for use in oil-in-watermeasurement which use UV fluorescence for detection, such asenviroFlu-HC sensors available from TriOS Optical Sensors (Oldenburg,Germany). The sensors may comprise lenses which are coated or otherwisetreated to prevent or limit the amount of fouling or film that occurs onthe lenses. When one or more sensors in the system generate a signalthat the concentration of one or more organic and/or inorganic compoundsexceeds a predetermined concentration, the control system can implementa responsive action such as a suitable feedback action or feedforwardaction, including but not limited to removing adsorbent material viawaste discharge port 216 (as indicated by dotted line connectionsbetween the controller 205 and the waste discharge port 216); adding newor regenerated adsorbent material via adsorbent material introductionapparatus 229 or at one of the other locations (as indicated by dottedline connections between the controller 205 and the adsorbent materialintroduction apparatus 229); adding a different type of adsorbentmaterial; modifying the hydraulic retention time; modifying thebiological characteristics such as simple carbon food formicro-organisms or adding phosphorus, nitrogen and/or pH adjustmentchemicals; and/or other modifications as described above or that will beapparent to those of ordinary skill in the art.

Note that while the controller 205 and the adsorbent materialintroduction apparatus 229 are shown only with respect to FIG. 2, it isintended that these features and the various feedback and feedforwardcapabilities can be incorporated in any of the systems described herein.In addition, the controller 205 can be electronically connected to othercomponents such as a wastewater feed pump and the suspension system 232.

After the mixed liquor is aerated and treated by the adsorbent materialin the biological reactor 202, the processed mixed liquor passes throughseparation subsystem 222, and is transferred to the membrane operatingsystem 204 substantially free of adsorbent material. The separationsubsystem 222 prevents adsorbent material from passing into the membraneoperating system 204. By maintaining the adsorbent material in thebiological reactor 202, or otherwise upstream of the membrane operatingsystem 204, the method and system of the present invention minimizes oreliminates the likelihood of fouling and/or abrasion of the membraneoperating system tank membranes by the adsorbent material.

The membrane operating system 204 contains filtering membranes 240 tofilter the biomass and any other solids in the mixed liquor in themembrane operating system tank 204 from the effluent from the bioreactor212. These membranes 240, which can be in the form of hollow fibermembranes or other suitable configurations, as is known to those ofordinary skill in the art, are typically very expensive and it is highlydesirable to protect them from damage in order to maximize their usefullife. In the method and system of the present invention, the life of themembranes in the operating system tank are extended, since theseparation subsystem 222 substantially reduces or eliminates entry ofthe adsorbent material such as granular activated carbon, and/or anyother solid granules and particles, into the membrane operating system204.

Outlet 212 transports filtered effluent from the membrane operatingsystem tank 204. Return activated sludge line 214 transports a returnactivated sludge stream from the membrane operating system tank 204 tothe biological reactor 202 for further use in processing of thewastewater feedstream. Excess sludge is wasted from the system usingwaste line 218 as in a conventional membrane biological reactor system.

In systems in which biological reactor 202 is an aerobic reactor such asan aeration tank and the micro-organisms are aerobic micro-organisms, anair diffusion apparatus or mechanical mixing system can be used tomaintain the adsorbent material in suspension. As described in furtherdetail below, various additional embodiments of the present inventioninclude alternative or supplemental suspension apparatus or system 232to maintain the adsorbent material in suspension.

Maintaining the relatively large granules of adsorbent material insuspension typically requires considerable more energy than a prior artsystem not using the adsorbent material, or that employs powderedactivated carbon. Nonetheless, the advantages of using granules ofadsorbent material according to the present invention, includingincreased rate and degree of contaminant removal, thereby minimizing orobviating the need for further downstream treatment, outweighs anyincrease in energy consumption for operating the system.

The suspension system 232 in certain embodiments of the presentinvention, utilizes one or more of jet mixing, mechanical mixing, jetaeration, coarse bubble aeration, and other types of mechanical or airsuspension to maintain the adsorbent material 234 in suspension whileminimizing attrition of the adsorbent material 234.

In certain embodiments, after an initial period of time in which theadsorbent material 234 is within the biological reactor 202 and somegranule breakage occurs, e.g., some of the rough and/or protrudingsurfaces of the adsorbent material 234 break off and becomes powder,fines, needles or other smaller particulates, the adsorbent material 234maintained in suspension by the jet suspension system 232 stabilizes,whereby little or no further breakage or degradation in size occurs.

In additional embodiments of the present invention, prior tointroduction of adsorbent material into the system, the material can bepreconditioned by removing easy-to-break portions of the adsorbentmaterial, thereby minimizing creation of fines and other undesirablesmaller particles that are difficult to separate and can abrade themembranes. Preconditioning can occur with or prior to pre-wetting, forinstance, in a suitable conditioning apparatus such as a wet or dryparticle tumbler.

The concentration of adsorbent material in the mixed liquor is generallydetermined based upon the specific system parameters and wastewater totreat the particular combination of biologically refractory and/orbiologically inhibitory organic or inorganic compounds to meet afacility's discharge requirements. Testing has indicated that operatinga membrane biological reactor with a typical industrial mixed liquorsuspended solids concentration (in a normal range for the particularmembrane biological reactor configuration employed) and an adsorbentmaterial concentration, such as granular activated carbon, of about 20%(of the total mixed liquor suspended solids concentration) was adequateto remove the biologically refractory and/or biologically inhibitoryorganic compounds present in the wastewater feed without creatingfouling problems on the screening system used. Higher concentrations ofadsorbent material can be added to provide an additional margin ofsafety against process upsets that could cause higher than normaleffluent concentrations of biologically refractory compounds,biologically inhibitory compounds, and/or organic or inorganic compoundsentirely resistant to biological decomposition. Note that thisadditional adsorbent material will result in increased screening and/orsettling requirements. The lowest concentration of adsorbent materialthat can be utilized and still achieve the required effluent quality canbe empirically determined, based upon a desired margin of safety againstprocess upsets that is based on experience or otherwise deemedappropriate for the particular system and process.

The present invention using adsorbent material upstream of a membraneoperating system tank to adsorb organic and inorganic materials(biologically refractory, biologically inhibitory or otherwise) as wellas to provide for a suspended media membrane biological reactor isapplicable for a variety of different configurations. In addition,various separation devices may also be used to maintain the adsorbentmaterial in the biological reactor. It will be appreciated by one ofordinary skill in the art that different systems will have differenteconomic benefits based on the individual characteristics of thewastewater and the region where the facility is to be installed.

The factors that are controlled to produce optimal treatment conditionsinclude the type of adsorbent material, including its size, shape,hardness, specific gravity, settling rate, requisite air flow or othersuspension needs for granule suspension in the mixed liquor, i.e., tomaintain the granular activated carbon as a suspended media, the screenbar spacing or opening size and hole configuration, the concentration ofadsorbent material in the mixed liquor, the concentration of the mixedliquor volatile suspended solids, the total concentration of mixedliquor suspended solids, the ratio of the return activated sludge flowrate divided by the flow rate of the mixed liquor entering the membraneoperating system tank, the hydraulic retention time and the sludgeretention time. This optimization provides adsorption of some portion ofthe biologically refractory compounds, easy to degrade biological oxygendemand compounds (BOD₅), biologically inhibitory compounds, organic orinorganic compounds entirely resistant to biological decomposition, andextra-cellular polymeric substances by the adsorbent material such asgranular activated carbon suspended in the mixed liquor.

Another benefit of the apparatus of the present invention is providingsites to which the micro-organisms in the mixed liquor suspended solidscan adhere. This aspect of the process produces a mixed liquor volatilesuspended solids stream that is more stable and resilient in itsresponse to upset conditions and allows enhanced biodegradation of theorganics present in the wastewater as compared to a non-granularactivated carbon enhanced membrane biological reactor operated withsimilar hydraulic retention times and sludge retention times. A sourceof micro-organisms inside the pore spaces, or on the surface, of theadsorbent material serves as a source of seed bacteria in the event ofan upstream process upset resulting in the loss of some of the viablemicro-organisms floating free in the mixed liquor. In the event of athermal or toxic chemical shock to the system, which would, inconventional systems, terminate certain bacteria, some of themicro-organisms within the pore spaces or on the surface can survive,thus only a fraction of the recovery time is necessary as compared toconventional systems without adsorbent. For instance, in systems wherethe bacteria is mesophilic, the adsorbent can allow some bacteria withinthe pore sites to survive in the event of thermal shock due to increasedtemperature. Likewise, in systems where the bacteria is thermophilic,the adsorbent allows some bacteria within the pore sites to survive inthe event of thermal shock due to decreased temperature. In both ofthese circumstances, the time required for the cultures to re-acclimatecan be greatly reduced. In addition, in the event of a system shock thatterminates all or a portion of the micro-organism population, thepresence of adsorbent material allows for continued operation, in whichlabile, refractory, and inhibitory contaminants can be adsorbed whilethe micro-organism population is adjusted.

The various benefits result in a more rapid acclimation of the mixedliquor to the wastewater feed, reduce fouling of the membranes, animproved tolerance to variations in feed concentrations and flow rate,produce a sludge that can be dewatered more quickly with a less oilynature that is easier to handle, and an effluent having a lowerconcentration of organic and inorganic impurities than can be obtainedfrom a conventional membrane biological reactor apparatus.

The use of an adsorbent such as granular activated carbon in place ofpowdered activated carbon eliminates the membrane fouling and/orabrasion that have been identified as a problem in powdered activatedcarbon membrane biological reactors testing.

Although the use of granular activated carbon in place of powderedactivated carbon does not use carbon as efficiently on a weight basis,the system and method of the present invention substantially preventsthe granular activated carbon from entering the membrane operatingsystem thereby minimizing or eliminating the likelihood of abrasion andfouling of the membranes. The impact of the reduced adsorptionefficiency as a result of using granular activated carbon in place ofpowdered activated carbon does not, however, significantly impact theefficacy of the overall activated carbon-enhanced membrane biologicalreactor apparatus.

Testing has indicated that the principal mechanism of removal of certainbiologically inhibitory organics and/or biologically refractorycompounds is related to an increase in the residence time that thebiologically refractory and biologically inhibitory compounds areexposed to the micro-organisms in the powdered activated carbon enhancedapparatus. Micro-organisms in the mixed liquor volatile suspended solidsadsorbed on the adsorbent material such as granular activated carbonhave a longer period of time to digest these certain biologicallyrefractory and biologically inhibitory compounds. Increased residencetime for biodegradation has been shown to be a major factor in reducingthe concentration of certain biologically refractory and biologicallyinhibitory compounds in the membrane biological reactor effluent, andthe higher adsorption efficiency of the powdered activated carbon is notrequired to achieve the desired results.

Granular activated carbon in a carbon-assisted membrane biologicalreactor performs as well or better than a powdered activated carbonenhanced membrane biological reactor in enhancing the removal ofbiologically refractory compounds, biologically inhibitory compounds,compounds that are entirely resistant to biological decomposition, andextra-cellular polymeric compounds. Also, because of its larger size, itcan be effectively filtered or otherwise separated from the mixed liquorthat enters the membrane operating system tank(s). The abrasion thatoccurs when using the powdered activated carbon can be eliminated orsignificantly reduced by employing granular activated carbon inaccordance with the present invention.

While the use of the powdered activated carbon particles in a membranebiological reactor has demonstrated some of the same advantagesdescribed above for the granular activated carbon system, the observedmembrane abrasion from the powdered activated carbon particles in themembrane operating system tank(s) is unacceptable since the membrane'suseful life can be reduced to an unacceptable level, e.g., significantlyless than a typical membrane warranty. Since the cost of the membranesrepresents a significant portion of the total cost of a membranebiological reactor system, an extension of their useful life is animportant factor in the operating cost of the membrane operating system.

FIG. 3 shows an alternative embodiment of a membrane biological reactorsystem 300 that utilizes a biological denitrification operation. Otherspecialized biological or chemical treatment systems required by aspecific influent wastewater can also be incorporated in the system ofthe present invention generally shown with respect to FIG. 2, as will beapparent to a person having ordinary skill in the art. The embodiment ofFIG. 3 is similar to the embodiment of FIG. 2, with the addition of ananoxic (low oxygen concentration) zone 331. In the embodiments hereinusing an anoxic zone or vessel, a simple organic carbon source, such asmethanol or the biochemical oxygen demand content of the wastewateritself, provides for the consumption by biological organisms. Wastewater306 is introduced into the anoxic zone 331, which is in fluidcommunication with the biological reactor 302 containing adsorbentmaterial 334. The anoxic zone 331 can include a mixer and/or an aerationdevice (not shown). In embodiments herein in which an aeration device isused, the dissolved oxygen concentration is controlled to maintainanoxic conditions. Effluent from the biological reactor 302 isintroduced via a separation subsystem 322 to an inlet 310 of themembrane operating system 304. In the membrane operating system 304, thewastewater passes through one or more microfiltration orultra-filtration membranes, thereby eliminating or minimizing the needfor clarification and/or tertiary filtration. Membrane permeate, i.e.,liquid that passes through the membranes 340, is discharged from themembrane operating system 304 via an outlet 312. Membrane retentate,i.e., solids from the biological reactor 302 effluent, includingactivated sludge, is returned to the anoxic zone 331 via a returnactivated sludge line 314. Spent adsorbent material from the biologicalreactor 302 can be removed via a mixed liquor waste discharge port 316of the biological reactor 302. A waste outlet 318 can also be connectedto the return pipe 314 to divert some or all the return activated sludgefor disposal, for instance, to control the concentration of the mixedliquor and/or culture. The mixed liquor waste discharge port 316 canalso be used to remove a portion of the adsorbent material. Anequivalent quantity of fresh or regenerated adsorbent material can beadded.

As in the system described in FIG. 2, there are multiple locations atwhich the adsorbent material 334 can be added to the system. In apreferred embodiment, adsorbent material is added at a location 330 bthat prevents passage into anoxic zone 331.

FIG. 4 is a schematic depiction of a water treatment system 400 which isone embodiment of a system 100 shown in FIG. 1. In system 400, abiological reactor 402 is divided or partitioned into multiple sections402 a and 402 b, e.g., using a baffle wall 403. A membrane operatingsystem 404 is positioned downstream of biological reactor 402.

The hydraulic flow between zones 402 a and 402 b is engineered toprovide a flow in the downstream direction. This can be accomplished byconfigurations and/or apparatus including, but not limited to anoverflow weir, submerged orifices, and/or various distribution pipingarrangements, for the purpose of maintaining positive separation betweenzones 402 a and 402 b and to maintain adsorbent material 434 only inzone 402 b. These various configurations can also be designed so as tocontrol the rate of flow between zones 402 a and 402 b. Further specificarrangements are not illustrated as these will be known to one ofordinary skill in the art.

During operation, an influent wastewater stream 406 is introduced intothe biological reactor 402, and in particular to the first zone 402 a ofthe biological reactor 402. As was discussed above, it will be apparentto a person having ordinary skill in the art, phosphorus, nitrogen, andpH adjustment materials or chemicals can be added to maintain optimalnutrient ratios and pH levels for the biological life and associatedactivity, including biological oxidation, in the first zone 402 a. Themicro-organisms in the first zone 402 a are capable of breaking down atleast a portion of the biologically labile content of the mixed liquorsuspended solids. The simple carbon, i.e., biologically labilecompounds, in the mixed liquor suspended solids serve as a food sourcefor the micro-organisms. Wastewater can be treated in zone 402 a toremove substantially all of the biologically labile content of the mixedliquor suspended solids, or, in certain embodiments, a portion of thebiologically labile content of the mixed liquor suspended solids can beretained for passage into the biological reaction zone 402 b. Inembodiments in which the biologically labile content of the mixed liquorsuspended solids is reduced in zone 402 a to a level that isinsufficient to efficiently support micro-organisms downstream, one ormore controls are implemented to maintain an effective concentration ofa micro-organism food source, particularly in the downstream biologicalreaction zone 402 b. This control can be, for instance, based on theresidence time of wastewater in the upstream zone 402 a, passing aslipstream of untreated influent wastewater directly to the zone 402 b,controlling the return activated sludge, introducing methanol or othersimple carbon food source for the micro-organisms, or provideintermittent aeration in zone 402 a, or other methods that promote ahealthy biomass in zone 402 b.

Adsorbent material 434 is maintained in suspension in biologicalreaction zone 402 b using a suspension apparatus 432, which can includeone or more of the suspension systems described herein, e.g., as shownin FIG. 7, 8, 9, 10, 11 or 12, in the examples herein, or any suitableconventional apparatus for circulating air, liquid or a combination ofair and liquid. These conventional apparatus include, but are notlimited to, air diffusion bubblers, paddles, mixers, surface aerators,liquid circulating pumps, and others that are known to one of ordinaryskill in the art. It should be appreciated that, while in certainembodiments it is desirable to use a suspension apparatus 432 havingrelatively low energy consumption to maintain the adsorbent material 434in suspension, such as those described in conjunction with FIG. 7, 8, 9,10, 11, or 12, or in Example 3, Example 4, or Example 5, otherembodiments using less efficient apparatus are also suitable, as theoverall volume of the zone 402 b within which adsorbent material 434must be maintained in suspension is only a portion of the total volumeof the biological reactor 402.

A screening/separation system 422 is positioned in section 402 b tosubstantially prevent passage of adsorbent material 434 to the membraneoperating system 404. In certain embodiments, adsorbent material isadded only at location 430 b, i.e., corresponding to zone 402 b.

Note that while system 400 is shown with one substantiallyadsorbent-free biological reactor zone, and one zone containingadsorbent material 434, it will be appreciated by one of ordinary skillin the art that a fewer or a greater number of zones of each type can beemployed. The concentration of adsorbent material 434 in section 402 bcan be the same concentration as employed, e.g., in the system of FIG.1, or a higher or lower concentration can be used depending on thewastewater being treated.

In addition, the biological reactor zones can be formed in variousconfigurations. For instance, in a prismatic biological reactor tank, apartition wall can be provided across the width of the tank to divide itinto zones. In a cylindrical tank, for example, a partition wall can beprovided as a chord, or plural walls, e.g., as radii, can be providedthat form two or more sectors.

By having adsorbent material only in the final biological reaction zoneor zones, biologically labile compounds can be treated in the upstreamsection without adsorbent material and hence without the need to suspendthe adsorbent material in the mixed liquor of the adsorbent-free zonesof system 400. This also permits development of a colony ofmicro-organisms that can biodegrade at least certain biologicallyrefractory and/or biologically inhibitory compounds that cannot bebiologically decomposed by the traditional microorganisms that wouldexist in the upstream sections of this system. It will also beappreciated by one of ordinary skill in the art that a system similar tosystem 400 can be provided according to the present invention usingseparate tanks rather than divided sections of a biological reactor, asshown schematically in FIG. 6, or a combination of divided sections of abiological reactor and separate vessels.

Still referring to FIG. 4, effluent from the biological reaction zone402 b is introduced via the screening/separation system 422 to an inlet410 of the membrane operating system 404. In the membrane operatingsystem 404, the wastewater passes through one or more microfiltration orultra-filtration membranes 440, and membrane permeate is discharged viaan outlet 412 while membrane retentate, including activated sludge, isreturned to the biological reaction zone 402 a via a return activatedsludge line 414.

Spent adsorbent material from the biological reaction zone 402 b can beremoved periodically via a mixed liquor waste discharge port 416. Awaste outlet 418 can also be connected to the return activated sludgeline 414 to divert some or all the return activated sludge for disposal,for instance, to control the concentration of the mixed liquor and/orculture. The mixed liquor waste discharge port 416 can also be used toremove a portion of the adsorbent material. An equivalent quantity offresh or regenerated adsorbent material can be added.

FIG. 5 shows a system 500 that operates in a manner similar to system400, with a biological reactor 502 that is divided into multiple zones502 a and 502 b, and includes a biological denitrification step that isintegrated with the biological reactor 502. In this embodiment,adsorbent material 535 added, e.g., a location 530 b, and is maintainedin suspension in zone 502 b and not introduced into the anoxic zone 531or zone 502 a.

Effluent from the biological reaction zone 502 b is introduced via thescreening/separation system 522 to an inlet 510 of the membraneoperating system 504. In the membrane operating system 504, thewastewater passes through one or more microfiltration orultra-filtration membranes 540, and membrane permeate is discharged viaan outlet 512 while membrane retentate, including activated sludge, isreturned to the anoxic zone 531 via a return activated sludge line 514.

Spent adsorbent material from the biological reaction zone 502 b can beremoved periodically via a mixed liquor waste discharge port 516. Awaste outlet 518 can also be connected to the return activated sludgeline 514 to divert some or all the return activated sludge for disposal,for instance, to control the concentration of the mixed liquor and/orculture. The mixed liquor waste discharge port 516 can also be used toremove a portion of the adsorbent material. An equivalent quantity offresh or regenerated adsorbent material can be added.

Under certain operational conditions, it may be necessary to introduce asimple organic carbon source, such as methanol to the anoxic zone, toassist with the denitrification process. Alternatively, the biologicaloxygen demand content of the raw wastewater can typically provide thenecessary food source for consumption by biological organisms.

In further embodiments, an anoxic zone can be provided downstream (notshown) of zone 502 b, or between zones 502 a and 502 b. In either case,it will likely be necessary to add a food source for consumption bybiological organisms in the anoxic zone to assist with thedenitrification process.

It will also be appreciated by one of ordinary skill in the art that asystem similar to system 500 can be provided according to the presentinvention using separate biological reactors rather than dividedsections of a biological reactor, as shown schematically in FIG. 6, or acombination of divided sections of a biological reactor and separatereactors.

FIG. 6 is a schematic depiction of another embodiment of a watertreatment system 600. In system 600, a series of biological reactors areprovided, including a first biological reactor 602 a that issubstantially free of adsorbent material, and a second biologicalreactor 602 b that contains a suspension of adsorbent material 634 thatcan be added, e.g., one or both of locations 630 a and 630 b. A membraneoperating system 604 is positioned downstream of biological reactor 602a and 602 b. The second biological reactor 602 b includes ascreening/separation system 622 is positioned in section 602 b tosubstantially prevent passage of adsorbent material to the membraneoperating system 604.

The hydraulic flow between reactors 602 a and 602 b is engineered toprovide a flow in the downstream direction to maintain adsorbentmaterial only in zone 602 b, i.e., to prevent backflow of adsorbentmaterial from reactor 602 b to reactor 602 a, and can be designed so asto control the rate of flow between zones 602 a and 602 b.

During operation, an influent wastewater stream 606 is introduced intothe biological reactor 602 a. Micro-organisms in the first biologicalreactor 602 a are capable of breaking down at least a portion of thebiologically labile compounds contained in the mixed liquor suspendedsolids. The simple organics in the mixed liquor suspended solids serveas a food source for the micro-organisms. The partially-treatedwastewater is passed via conduit 607 to the biological reactor 602 b.Partially-treated wastewater from the biological reactor 602 a can alsobe gravity-fed to the biological reactor 602 b, or passed by other meansknow to those having ordinary skill in the art.

Wastewater can be treated in the first biological reactor 602 a toremove substantially all of the biologically labile compounds of themixed liquor suspended solids, or, in certain embodiments, a portion ofthe biologically labile compounds contained in the mixed liquorsuspended solids can be retained for passage into the second biologicalreactor 602 b. In embodiments in which the biologically labile compoundscontained in the mixed liquor suspended solids is reduced in the firstbiological reactor 602 a to a level that is insufficient to efficientlysupport micro-organisms downstream, one or more controls are implementedto maintain an effective concentration of a micro-organism food source,particularly in the downstream biological reactor 602 b. This controlcan be, for instance, based on the residence time of wastewater in theupstream biological reactor 602 a, passing a slipstream of untreatedinfluent wastewater directly to the biological reactor 602 b,controlling the return activated sludge, introducing methanol or othersimple carbon food source for the micro-organisms, or other suitablefeedback or feedforward action.

Adsorbent material 634 is maintained in suspension in the biologicalreactor 602 b using a suspension apparatus 632, which can include one ormore of the suspension systems described herein, e.g., as shown in FIG.7, 8, 9, 10, 11 or 12, in the examples herein, or any suitableconventional apparatus for circulating air, liquid or a combination ofair and liquid. These conventional apparatus include, but are notlimited to, air diffusion bubblers, paddles, mixers, surface aerators,liquid circulating pumps, and others that are known to one of ordinaryskill in the art. It should be appreciated that, while in certainembodiments it is desirable to use a suspension apparatus 632 havingrelatively low energy consumption to maintain the adsorbent material insuspension, such as those described in conjunction with FIG. 7, 8, 9,10, 11 or 12, or in Example 3, Example 4, or Example 5, otherembodiments using less efficient apparatus are also suitable, as theoverall volume of the zone 602 b is only a portion of the total combinedvolume of the biological reactors 602 a and 602 b.

The screening/separation system 622 is positioned in biological reactor602 b to substantially prevent passage of adsorbent material 634 to themembrane operating system 604. In certain instances, adsorbent material634 is added only to the biological reactor 602 b, e.g., at location 630a associated with the conduit 607, or directly into the biologicalreactor 602 b (location 630 b). In certain preferred embodiments,adsorbent material is pre-wetted, e.g., to form a slurry, prior tointroduction into the biological reactor 602 b.

Note that while system 600 is shown with one substantiallyadsorbent-free biological reactor, and one biological reactor containingadsorbent material 634, it will be appreciated by one of ordinary skillin the art that a fewer or a greater number of biological reactors, orsections of biological reactors, of each type can be employed. Theconcentration of adsorbent material in biological reactor 602 b can bethe same concentration as employed, e.g., in the system of FIG. 1, or ahigher concentration can be used, depending on factors including but notlimited to the characteristics of the partially-treated wastewater to betreated in biological reactor 602 b.

By having adsorbent material only in the final biological reactor,biologically labile compounds can be treated in the upstream biologicalreactor without adsorbent material. This permits development of a colonyof micro-organisms that can biodegrade the biologically refractoryorganisms that cannot be biologically oxidized by the traditionalmicroorganisms that would exist in the upstream sections of this system.It will also be appreciated by one of ordinary skill in the art that asystem similar to system 600 can be provided according to the presentinvention using divided sections of a biological reactor rather thanseparate biological reactors, as shown schematically in FIG. 4, or acombination of divided sections of a biological reactor and separatereactors.

Still referring to FIG. 6, effluent from the biological reactor 602 b isintroduced via the screening/separation system 622 to an inlet 610 ofthe membrane operating system 604. In the membrane operating system 604,the wastewater passes through one or more microfiltration orultra-filtration membranes 640, and membrane permeate is discharged viaan outlet 612 while membrane retentate, including activated sludge, isreturned to the biological reactor 602 a via a return activated sludgeline 614.

Spent adsorbent material from the biological reactor 602 b can beremoved periodically via a mixed liquor waste discharge port 616. Awaste outlet 618 can also be connected to the return pipe 614 to divertsome or all the return activated sludge for disposal, for instance, tocontrol the concentration of the mixed liquor and/or culture.

Referring generally to FIGS. 7, 8, 9, 10 and 11, various alternativeembodiments are shown including a jet suspension system in which mixedliquor (including MLSS having MLVSS) and adsorbent dispersed therein iscirculated through a jet nozzle. This circulation provides for intimatemixing of the adsorbent and the mixed liquor, and also providesturbulence that maintains the adsorbent in suspension in the biologicalreactor. The turbulence can be localized turbulence, e.g., proximate thenozzle orifice, causing swirling and rolling of the fluid exiting thejet nozzle. In FIGS. 7, 8 and 11, solid black elements representadsorbent material, and irregular linear elements representmicro-organisms or biomass.

FIG. 7 schematically depicts a suspension apparatus 732 within abiological reactor 702 (a portion of which is shown in the figure forclarity of exposition). The suspension apparatus 732 comprises a jetnozzle 744 fluidly connected to a pump 748 and a source 760 of gas. Thegas can be an oxygen-containing gas in the case of an aerobic biologicalreactor 702, or a gas free of oxygen or substantially free of oxygen inthe case of an anaerobic biological reactor 702.

The configuration shown in FIG. 7, and in certain additional embodimentsdescribed in conjunction with FIGS. 8, 9 and 10, can be deployed using,for instance, the Vari Cant® system that is commercially available fromSiemens Water Technologies of Rothschild, Wis., USA. Other jet aerationsystems can also be deployed for one or more of the systems shown withrespect to FIGS. 8, 9 and 10. For instance, various systems include, butare not limited to, jet aeration systems that are commercially availablefrom Fluidyne Corporation of Cedar Falls, Iowa, USA; KLa Systems ofAssonet, Mass., USA; and Mixing Systems Inc. of Dayton, Ohio, USA.

Note that while the systems described herein with respect to FIGS. 7, 8,9, 10, and 11 generally depict a pump outside of the biological reactortank, a person having ordinary skill in the art will appreciate that oneor more pumps can also be positioned inside of the tank(s). In furtherembodiments, one or more pumps can be positioned inside or outside of ahead tank to maintain positive suction.

In addition, while the systems described herein with respect to FIGS. 7,8, 9, 10 and 11 generally show, for purposes of illustration, the entirejet nozzle positioned in the biological reactor tank, in certainembodiments a portion of the jet nozzle(s) can be positioned outside ofthe biological reactor tank, with at least their outlet orifice(s)located in the biological reactor tank.

The jet nozzle 744 liquid inlet 746 and outlet orifice 764, and the pumpapparatus 748 inlet 752 and outlet 754, are dimensioned and configuredto allow passage of adsorbent material and MLSS, including MLVSS.Accordingly, a mixture of mixed liquor, including MLSS and MLVSS, andadsorbent material is drawn from an outlet 750 of the biological reactor702 into an inlet 752 of the pump apparatus 748 through a line 751. Themixture is pumped out of the pump apparatus 748 via an outlet 754,through a line 755 and directed to a liquid inlet 746 integral with orotherwise in fluid communication with the jet nozzle 744.

Simultaneously, gas 760 is directed through line 761 to a gas inlet 758integral with or otherwise in fluid communication with the jet nozzle744 and is directed to a mixing chamber 766, where it expands andimparts motive energy to the mixed stream of mixed liquor and dispersedadsorbent material in the direction of the nozzle outlet orifice 764.The expanded gas, mixed liquor and dispersed adsorbent material passthrough a throat 768 having decreasing cross-sectional area in adirection of fluid flow, in which the velocity is increased, and out ofthe outlet orifice 764. The combined stream of gas, liquid, and solidparticles forcefully enters the biological reactor 702, and the solidgranules of adsorbent material remain in suspension under continuousoperation due to the liquid turbulence in the biological reactor 702.

Referring now to FIG. 8, another embodiment of a biological reactor isshown including a jet suspension system. In particular, a biologicalreactor 802 includes a jet suspension system 832 including a jet nozzle844 having at least an outlet orifice 864 located in the biologicalreactor 802 for circulating mixed liquor having adsorbent materialdispersed therein. The jet nozzle 844 is fluidly connected to a pump 848to circulate mixed liquor having adsorbent material dispersed therein tocreate turbulence that maintains the adsorbent material in suspension.Any jet mixer, sprayer or other device capable of directing anddischarging the mixed liquor having adsorbent material dispersed thereinwithout requiring a gas inlet can be used as the jet nozzle 844 as willbe appreciated by one having ordinary skill in the art.

In aerobic biological reactors 802, a source of oxygen-containing gas isalso provided (not shown), such as a conventional air diffusionapparatus.

The liquid inlet 846 and outlet orifice 864 of the jet nozzle 844, andthe inlet 852 and outlet 854 of the pump apparatus 848, are dimensionedand configured to allow passage of adsorbent material and mixed liquorsuspended solids, including mixed liquor suspended volatile solids.Accordingly, a mixture of mixed liquor, including MLSS and MLVSS, andadsorbent material is drawn from an outlet 850 of the biological reactor802 into inlet 852 of the pump apparatus 848 through a line 851. Themixture is pumped out of the pump apparatus 848 via outlet 854, througha line 855 and directed to a liquid inlet 846 integral with or otherwisein fluid communication with the jet nozzle 844. The jet nozzle 844includes a throat portion 868 having decreasing cross-sectional area ina direction of fluid flow to increase velocity of mixed liquor andadsorbent material exiting an outlet orifice 864.

Referring generally to FIGS. 9, 10 and 11, alternative embodiments areshown including a jet suspension system in which mixed liquor and/orreturn activated sludge is circulated through a jet nozzle withoutadsorbent material. This circulation provides for intimate mixing of theadsorbent material and the mixed liquor at the outlet of the jet nozzle,and also provides turbulence that maintains the adsorbent material insuspension within the biological reactor. The turbulence can belocalized turbulence, e.g., proximate the nozzle orifice, causingswirling and rolling of the fluid exiting the jet nozzle.

FIG. 9 schematically depicts a wastewater treatment system 900 includinga suspension apparatus 932 within a biological reactor 902 and upstreamof a membrane operating system 904. The suspension apparatus 932comprises a jet nozzle 944 fluidly connected to a pump 948 and a source960 of compressed gas. The system 900 includes a screening/separationsystem 922 which prevents passage of at least a majority of adsorbentmaterial, for instance, at the outlet 908 of the biological reactor 902.

In certain embodiments, mixed liquor is drawn from the effluent of thebiological reactor 902 into an inlet 952 of the pump apparatus 948through conduits 972, 970, wherein conduit 972 is between the outlet 908of the biological reactor 902 and the inlet 910 of the membraneoperating system 904. In additional embodiments, return activated sludgeis drawn from a conduit 914 from the membrane operating system 904 intoline 970 into the inlet 952 of the pump apparatus 948. In furtherembodiments, a combined stream of effluent from the biological reactor902 and return activated sludge from the membrane operating system 904is used as the liquid providing circulation to the pump. Liquid from theeffluent and/or the return activated sludge is pumped out of the pumpapparatus 948 through a line 955 and directed to a liquid inlet integralwith or otherwise in fluid communication with the jet nozzle 944. Inconjunction, compressed gas 960 is directed through line 961 to a gasinlet integral with or otherwise in fluid communication with the jetnozzle 944 and is directed to a mixing chamber 966, where it expands andimparts motive energy to the mixed liquor in the direction of the nozzleoutlet orifice 964. The expanded gas and mixed liquor pass through athroat 968 having decreasing cross-sectional area in a direction offluid flow, in which the velocity is increased, and out of the outletorifice 964. The combined stream of gas and liquid forcefully enters thebiological reactor 902, and the solid granules of adsorbent materialremain in suspension under continuous operation due to turbulence in thebiological reactor 902.

FIG. 10, schematically depicts another embodiment of a wastewatertreatment system, in which wastewater treatment system 1000 includes asuspension apparatus 1032 within a biological reactor 1002 and upstreamof a membrane operating system 1004. The system 1000 includes ascreening/separation system 1022 which prevents passage of at least amajority of adsorbent material, for instance, at the outlet 1008 of thebiological reactor 1002. The suspension apparatus includes a jet nozzle1044 fluidly connected to a pump 1048 to circulate mixed liquor tocreate turbulence that maintains the adsorbent in suspension. In aerobicbiological reactors 1002, a source of oxygen-containing gas is alsoprovided (not shown), such as a conventional air diffusion apparatus orany number of other devices that can transfer oxygen into the mixedliquor as would be apparent to one of ordinary skill in the art.

The liquid flow in system 1000 is similar to that of system 900 shownand described with respect to FIG. 9 above. Accordingly, in certainembodiments, mixed liquor is drawn from the effluent of the biologicalreactor 1002 into an inlet 1052 of the pump apparatus 1048 throughconduits 1072, 1070, wherein conduit 1072 is between the outlet 1008 ofthe biological reactor 1002 and the inlet 1010 of the membrane operatingsystem 1004. In additional embodiments, return activated sludge is drawnfrom a conduit 1014 from the membrane operating system 1004 into line1070 into the inlet 1052 of the pump apparatus 1048. In furtherembodiments, a combined stream of effluent from the biological reactor1002 and return activated sludge from the membrane operating system 1004is used as the liquid providing circulation to the pump.

Liquid from the effluent and/or the return activated sludge is pumpedout of the pump apparatus 1048 through a line 1055 and directed to aliquid inlet integral with or otherwise in fluid communication with thejet nozzle 1044. The mixed liquor passes through a throat 1068 havingdecreasing cross-sectional area in a direction of fluid flow, in whichthe velocity is increased, and out of the outlet orifice 1064. Theliquid stream forcefully enters the biological reactor 1002, and thesolid granules of adsorbent material remain in suspension undercontinuous operation due to turbulence in the biological reactor 1002.

In certain embodiments of systems 900 and 1000, it can be necessary todesign the hydraulics of the system so that the flow rate through thepump is equal to, or greater than the overall flow rate through thesystem, i.e., represented by the flow rate of the influent 906, 1006 andthe effluent 912, 1012.

FIG. 11 schematically depicts a suspension apparatus 1132 within abiological reactor 1102 (a portion of which is shown in the figure forclarity of exposition). The suspension apparatus 1132 comprises a jetnozzle 1144 fluidly connected to a pump 1148 and a source 1160 of gas.The gas can be an oxygen-containing gas in the case of an aerobicbiological reactor 1102, or a gas free of oxygen or substantially freeof oxygen in the case of an anaerobic biological reactor 1102.

An outlet 1150 of the biological reactor 1102 includes a screeningapparatus 1170 which prevents passage of at least a majority ofadsorbent material. A spray nozzle 1172 or other suitable apparatus isprovided to remove build-up from the screening apparatus 1170. Spaynozzle 1172 can direct gas and/or liquid to clear the screeningapparatus. In certain embodiments (not shown), spray nozzle 1172 can beconnected to a pump and/or the source 1160 of compressed gas, to providepressurized fluid to clear the screening apparatus 1170. In additionalembodiments, the spray nozzle 1172 can be eliminated, for instance, whenthe screening apparatus 1170 is an active screening device such as arotary screen or the like that prevents build-up of adsorbent material.

Accordingly, mixed liquor, including MLSS and MLVSS, that issubstantially free of adsorbent material is drawn from the outlet 1150of the biological reactor 1102 into an inlet 1152 of the pump apparatus1148 through a line 1151. Mixed liquor is pumped out of the pumpapparatus 1148 via an outlet 1154, through a line 1155 and directed to aliquid inlet 1146 integral with or otherwise in fluid communication withthe jet nozzle 1144. In conjunction, compressed gas 1160 is directedthrough line 1161 to a gas inlet 1158 integral with or otherwise influid communication with the jet nozzle 1144 and is directed to a mixingchamber 1166, where it expands and imparts motive energy to the mixedliquor in the direction of the nozzle outlet orifice 1164. The expandedgas and mixed liquor pass through a throat 1168 having decreasingcross-sectional area in a direction of fluid flow, in which the velocityis increased, and out of the outlet orifice 1164. The combined stream ofgas and liquid forcefully enters the biological reactor 1102, and thesolid granules of adsorbent material remain in suspension undercontinuous operation due to turbulence in the biological reactor 1102.

In certain embodiments of the wastewater treatment system describedherein, the system includes a gas lift suspension system which maycomprise one or more draft tubes or one or more other configurations.The one or more draft tubes may be sized and shaped for a desiredapplication and volume of a vessel, such as a biological reactor orother apparatus, to perform one or more of suspending the adsorbentmaterial, maintaining the adsorbent material in suspension, mixing theadsorbent material throughout the vessel, and aerating the environmentof the vessel, which may include aerobic microorganisms. The gas liftsuspension system may be constructed of various sizes and shapes basedon the size and shape of the vessel into which it is placed. The gaslift suspension system may comprise one or more draft tubes positionedwithin a vessel in which an adsorbent material is incorporated into thewastewater treatment system. As used herein, a “draft tube” may be atube or other structure having one or more sidewalls open at both endswhich when positioned in a vessel provides a passageway for fluid flowand may include solid particle suspension, for example, the suspensionof adsorbent material and related solids in a wastewater or mixed liquorwith air or other gas.

The draft tube may be constructed of any material suitable for aparticular purpose as long as it is abrasion resistant, resistant towastewater components at typical conditions for wastewater treatment,and able to withstand turbulent flows through and around the draft tube.For example, the draft tube may be formed of the same material as thevessel or may be formed of other lighter and less expensive materials,such as plastics, including fiberglass reinforced plastics, polyvinylchloride (PVC), or acrylic. The draft tube may be preformed forinsertion into the vessel, or manufactured as part of the vessel. Assuch, the draft tube may be designed to retrofit current systems. Thegas lift suspension system may be supported on a wall of the vessel, ormay be supported by a bottom portion of the vessel so long as it allowsfor flow through and around the draft tube. Alternatively, the gas liftsuspension system may be supported by an additional structureconstructed and arranged to retain and suspend the one or more drafttubes within the vessel.

An individual draft tube may be sized and shaped according to a desiredapplication, such as to suspend an adsorbent material within the vesseland/or to operate within a preselected time period for operation. Thedraft tube may also be sized and shaped to provide a desired level ofagitation within the draft tube to adequately suspend the adsorbentmaterial within the vessel or to aerate the environment of the vessel.The desired gas lift suspension system volume may be provided by asingle draft tube or by multiple draft tubes having a total volumesubstantially equal to the desired volume. A particular ratio of gaslift suspension system volume to vessel volume may be selected toprovide optimal suspension of the adsorbent material within the drafttube. An individual draft tube may have a cross sectional area of anyshape, such as circular, elliptical, square, rectangle, or any irregularshape. The individual draft tube may have any overall shape, such asconical, rectangular and cylindrical. In one embodiment, the draft tubeis a cylinder. The overall dimensions of the draft tube, such as length,width, and height, may be selected to provide optimal suspension of theadsorbent material within the vessel. For example, particular ratios ofdraft tube length to draft tube width or diameter may be selected toachieve optimal suspension of the adsorbent material within the vessel.The draft tube may be comprised of two opposed sidewalls within a vesselin a construction referred to as a “trough.” One or both ends of thedraft tube may be constructed and arranged to assist flow of adsorbentmaterial into and/or out of the draft tube. For example, the side wallat a first end of the draft tube may include one or more openingsforming passageways to allow some of the adsorbent material, wastewater,or other contents of the vessel that are located at or near the firstend of the draft tube to enter or exit through the sidewall of the drafttube. The openings forming the passageways may have any shape to allowfor sufficient suspension of the adsorbent material within the vessel.For example, openings may be triangular, square, semicircular or have anirregular shape. Multiple passageways may be identical to one anotherand uniformly positioned about the first end of the draft tube toequally distribute flow of adsorbent material in the draft tube.

The one or more draft tubes may be positioned at any suitable locationwithin the vessel so long as they provide adequate suspension of theadsorbent material within the vessel. For example, a single draft tubemay, but need not, be positioned centrally in relation to the vesselsidewalls. Similarly, multiple draft tubes in a single vessel may berandomly positioned or positioned in a uniform pattern in relation tothe vessel sidewalls. Multiple draft tubes in a single vessel may, butneed not be identical in volume or cross sectional area. For example, asingle vessel may comprise cylindrical, conical and rectangular drafttubes of varying height and cross sectional area. In one embodiment, avessel may have a first draft tube centrally positioned having a firstcross sectional area and a plurality of second draft tubes positionedadjacent to the side wall of vessel in which each of the second drafttubes has a second cross sectional area smaller than the first crosssectional area. In another embodiment, a vessel has a plurality ofidentical draft tubes. In yet another embodiment, a first draft tube maybe positioned within a second draft tube. In this embodiment, thebottoms of the draft tubes may be aligned with each other, or may beoff-set from one another.

In another embodiment, the draft tube may include a baffle to promotethe suspension of adsorbent material. The baffle may have any size andshape suitable for a particular draft tube. For example the baffle maybe a plate suitably positioned on an inner surface of the draft tube ora cylinder positioned in the draft tube. In one embodiment, the bafflemay be a solid or hollow cylinder centrally positioned within the drafttube. In another embodiment, the baffle may be a skirt that ispositioned at a first end or second end of one or more draft tubes inthe gas lift suspension system. The baffle may be constructed of thesame material as the draft tube, or a different material that iscompatible with the suspension system.

The vessel into which the draft tube may be placed may be of any size orshape suitable to suspend adsorbent material in conjunction with the gaslift suspension system. For example, the vessel may have a crosssectional area of any shape, such as circular, elliptical, square,rectangle, or any irregular shape. In some embodiments, the vessel maybe constructed or modified in order to promote suitable suspending ofthe adsorbent material. In certain embodiments, the vessel may beconstructed or modified to include sloped portions at the base of thevessel to promote the movement of adsorbent material toward the gas liftsuspension system. The sloped portions may be at any angle relative tothe base of the vessel to promote movement of the adsorbent materialtowards the gas lift suspension system.

Referring now to FIG. 12, an example of a gas lift suspension system1232 for maintaining adsorbent material in suspension within a vesselsuch as biological reactor 1202 is schematically depicted according toone embodiment. In FIG. 12, circular elements represent bubbles of gas,small solid elements or dots represent adsorbent material and irregularlinear elements represent micro-organisms or biomass. The gas liftsuspension system 1232 includes one or more draft tubes 1292 configured,positioned and dimensioned to facilitate lifting of adsorbent materialand maintaining the adsorbent material in suspension, as describedabove. Gas enters through a gas conduit 1290 and is directed into abottom portion of the draft tube(s) 1292 via distribution nozzles ordiffusers 1291. In certain alternative embodiments, gas can be directedinto the bottom portion of the draft tube(s) 1292 via apertures in thegas conduit 1290 rather than, or in conjunction with, the distributionnozzles or diffusers 1291. The gas from conduit 1290 can be introducedinto the vessel or biological reactor 1202 at the designated location(s)in a manner similar to a coarse bubble diffuser, and serves both as asource of oxygen or other gas for support of the micro-organism adheredto the adsorbent material and separate from the adsorbent material inthe mixed liquor, and as a source of lift force for maintaining theadsorbent material and biomass in suspension in the biological reactor1202. In particular, the gas provides upward lift as a result of itsbeing contained in the draft tubes 1292. As the gas bubbles rise insideof the draft tubes, they cause an upward flow that provides suction onthe bottom of the tube. This is the motive force used to draw the mixedliquor and adsorbent material through the tubes and lift it intosuspension in the tank. The gas circulation provides adequate lift inthe draft tubes to keep the contents of the tank sufficiently agitatedsuch that the settling of adsorbent material is minimized or eliminated.

In addition, the arrangement of FIG. 12 provides adequate mixing andsuspension with significantly less energy requirements as compared toother mixing and suspension systems. For example, the energy requiredfor a gas lift system 1232 in a biological reactor 1202 using adsorbentmaterial can be as low as one-tenth of the energy required withalternative suspension systems and may only require the gas necessaryfor the biological system.

Although the gas lift suspension system 1232 is shown and described inthe context of a plurality of draft tubes configured and positionedproximate a source of gas, alternative structures can be employed, suchas one or more troughs within a biological reactor, or other suitablestructure that produces the gas lift phenomenon described above.Additionally, the directional arrows shown in FIG. 12 are merelyillustrative of one possible way in which fluid flows throughout thesystem, and depending on the parameters of the system, including thesize and shape of the vessel, the size, shape and number of draft tubes,and air flow rate, the fluid may flow through the system in any numberof ways.

FIGS. 13A and 13B show additional embodiments of the present inventionincorporating a settling zone 1382 as a portion of a separationsubsystem. In FIGS. 13A and 13B, solid black elements representadsorbent material, and irregular linear elements representmicro-organisms or biomass. A biological reactor 1302 comprises an inlet1306 for receiving wastewater to be treated and an outlet 1308 fluidlyconnected to a membrane operating system (not shown). The settling zone1382, e.g., a quiescent zone, is proximate the outlet 1308 and isgenerally defined by baffles 1380 and 1381, which are positioned anddimensioned to direct adsorbent material away from the settling zone1382. The combined mixture of liquid and adsorbent material that flowsover baffle 1380 settles, since turbulence due to the jet aeration orother suspension system in the biological reactor 1302 is substantiallyreduced in the settling zone 1382. Adsorbent material having a greaterdensity than the suspended biological solids settles, and as it leavesthe settling zone 1382, is returned to suspension by the turbulenceoutside of the settling zone 1382 caused by the suspension system. Asshown in FIG. 13A, a screening apparatus 1322 is also provided proximatethe outlet 1308. The quantity of adsorbent blocked by the screeningapparatus 1322 is minimized due to the adjacent settling zone 1382. Incertain preferred embodiments, screening apparatus 1322 is placed withinthe baffle system at a distance from the baffles that is sufficient toensure that most of the adsorbent material will separate/settle from themixed liquor before it reaches the screen. Consequently, the screeningapparatus 1322 will receive fewer adsorbent particles which couldpotentially adhere to the screen surface and accelerate plugging/foulingof the screen. When screening systems are used in combination withbaffle systems, the plugging/fouling potential of the screen will begreatly reduced, as will the frequency of screen cleaning.

However, it is contemplated that in certain embodiments, the screeningapparatus 1322 can be eliminated altogether. The use of baffles aroundthe outlet 1308 of the aeration tank reduces the mixing energy impartedby the suspension apparatus and leaves the settling zone 1382 free ofturbulence and rising air bubbles, so that the denser adsorbent granulescan separate from the mixed liquor prior to its exiting the tank by wayof the effluent launderers. The baffling system allows the denseadsorbent material to separate from the mixed liquor, while at the sametime, directs the mixed liquor back into the mixing zone in the aerationtank.

Alternative settling zone systems within the biological reactor are alsocontemplated. For example, any of the previously-mentioned screens canbe used, or, as described in further detail below, a weir can be usedinstead of screening apparatus 1322.

The settling zone in combination with shearing action provided bypumping, mixing or jet aeration allows the adsorbent material that hashad the excess biomass sheared therefrom to settle in an area withoutmixing. The adsorbent material will settle to the bottom of this areaand re-enter the mixed liquor.

FIG. 13B shows another embodiment of a settling zone having a weir 1323.Low density biomass overflows the weir 1323 and the adsorbent settles.As adsorbent drops out of the quiescent zone, it mixes with the agitatedcontents of the tank including mixed liquor suspended solids andadsorbent and is re-suspended.

In embodiments of the present invention including a settling zone havingan adsorbent material waste discharge port, the waste discharge port canadvantageously be located proximate the settling zone. This allows thewaste adsorbent material to be removed while minimizing removal of mixedliquor.

Useful adsorbent materials for the present invention include varioustypes of carbons, such as activated carbon. In particular, granularactivated carbons are very effective, since the size range and densitiesof the granules can be selected to enable their retention in apredetermined portion of the system and thereby substantially preventthem from fouling and/or abrading the membranes.

In systems in which the granular activated carbon is not subjected tosignificant shearing forces and/or inter-granule collision, the granularactivated carbon can be produced from wood, coconut, bagasse, sawdust,peat, pulp-mill waste, or other cellulose-based materials. One suitableexample is MeadWestvaco Nuchar® WV B having nominal mesh sizes of 14×35(based on the U.S. Standard Sieve Series).

In additional embodiments, particularly those in which shearing actionis provided by turbulence and/or inter-granule collisions in a pumpand/or jet nozzle, use of adsorbent material(s) having higher hardnessvalues are desirable. For instance, granular activated carbons derivedfrom bitumen or coal-based materials are effective. In a particularembodiment, the granular activated carbon is derived from lignite.

Carbon materials can also be provided which are modified with atreatment process and/or species thereby providing an affinity tocertain chemical species and/or metals in the wastewater. For instance,in wastewaters having a relatively high level of mercury, at least aportion of the adsorbent material preferably includes granular activatedcarbon impregnated with potassium iodide or sulfur. Other treatmentsand/or impregnated species can be provided to target specific metals,other inorganic compounds and/or organic compounds.

In addition, the adsorbent can be a material other than activatedcarbon. For instance, iron-based compounds or synthetic resins can beused as the adsorbent materials, alone or in combination with otheradsorbent materials, e.g., in combination with granular activatedcarbon. Further, treated adsorbent materials other than activated carbonthat target certain metals, other inorganic compounds or organiccompounds can be used. For instance, in wastewaters having relativelyhigh levels of iron and/or manganese, at least a portion of theadsorbent can comprise a granular manganese dioxide filtering media. Inwastewaters having arsenic, at least a portion of the adsorbent cancomprise granular iron oxide composites. In wastewaters including leador heavy metals, at least a portion of the adsorbent can includegranular alumino-silicate composites.

In one embodiment, the adsorbent material can be selected based upon adesired specific gravity range. In order to maintain the adsorbentmaterial in suspension within acceptable energy consumption/cost ranges,specific gravity ranges relatively close to that of the wastewater aredesirable. On the other hand, in embodiments in which separation isbased at least in part on settling of the material, higher specificgravities are suitable. In general, the specific gravity is preferablygreater than about 1.05 in water at 20° C. In certain embodiments, thespecific gravity is greater than about 1.10 in water at 20° C. Asuitable upper limit for the specific gravity is, in certainembodiments, about 2.65 in water at 20° C.

Therefore, the adsorbent material having a specific gravity range isselected which provides sufficient suspension and therefore sufficientcontact with the wastewater and its contaminants. In addition, incertain embodiments, the specific gravity range provides sufficientsettling characteristics for subsequent removal of the adsorbentmaterial from the wastewater. In further embodiments, selection of thespecific gravity of the adsorbent material is based on minimization ofthe energy required to maintain the adsorbent material in suspension.

Furthermore, the desired adsorbent material, such as granular activatedcarbon, has a hardness level that minimizes creation of fines and otherparticulates due to inter-granule collisions and other process effects.

The size of the adsorbent material that the separation subsystem isdesigned to retain and thereby prevent its passage into the membraneoperating system is optimized to minimize the amount of adsorbentmaterial and fines entering the membrane operating system. Therefore,the method and system of the invention minimizes abrasion and fouling bycarbon granules or other granular materials impinging on the membranes,while still providing the operational advantages associated with the useof adsorbent material including activated carbon.

Suitable granule sizes for the adsorbent material are selected tocomplement the selected screening/separation methods, and the needs ofthe particular wastewater being treated. In certain preferredembodiments, the bottom limit of effective granule size of the adsorbentmaterial is selected such that it can easily be separated from the flowof mixed liquor entering the membrane operating system tank(s) in whichthe membranes are located. In general, the effective granule size of theadsorbent material has a bottom limit of about 0.3 millimeters, wheregreater than about 99.5 weight % of the adsorbent material is above thebottom limit; preferably having a lower limit of about 0.3 millimetersto an upper limit of about 2.4 millimeters (corresponding to a mesh size50 to a mesh size 8, based on United States Standard Sieve Series),where greater than 99.5 weight % of the adsorbent material is within thelower and upper limit; and in certain preferred embodiments about 0.3millimeters to about 1.4 millimeters (corresponding to a mesh size 50 toa mesh size 14, based on the United States Standard Sieve Series) wheregreater than about 99.5 weight % of the adsorbent material is within thelower and upper limit. It has been demonstrated that a granularactivated carbon with a minimum effective granule size of about 0.5millimeters to about 0.6 millimeters can be easily and efficientlyscreened from the mixed liquor with a suitable separation system, andsuch effective sizes, in granular activated carbon of suitabledensities, also can economically be maintained in suspension.

EXAMPLES

The present invention will now be illustrated by the followingnon-limiting examples.

Example 1

A pilot scale programmable logic controlled membrane biological reactorsystem (Petro™ MBR Pilot Unit available from Siemens Water Technologies,Rothschild, Wis., USA) having an aeration tank with an anoxic section,with an capacity of approximately 3,785 liters (l) (1,000 gallons (gal))and a membrane operating system equivalent to a commercial membranebiological reactor system, was modified to accommodate the granularactivated carbon addition described in the present invention. A wedgewire screen was situated at the inlet of a pump that transferred mixedliquor from the aeration tank to the membrane operating system.

A base synthetic feedstock included water having the followingconcentrations of organic/inorganic matter: 48 grams per liter (g/l) (48ounces per cubic foot (oz/cf)) of sodium acetate; 16 g/l (16 oz/cf) ofethylene glycol; 29 g/l (29 oz/cf) of methanol; 1.9 g/l (1.0 oz/cf) ofammonium hydroxide; and 0.89 g/l (0.89 oz/cf) of phosphoric acid. Theammonium hydroxide and phosphoric acid were sources for proper nutrientbalance for the bacteria within the membrane biological reactor system.

A sample wastewater mixture was prepared having high concentrations ofbiologically refractory and/or biologically inhibitory organiccompounds. Specifically, the sample wastewater mixture containedfollowing concentrations of biologically refractory and/or biologicallyinhibitory organic compounds: 90 milligrams per liter (mg/l) (0.09ounces per cubic foot (oz/cf) of EDTA; 30 milligrams per liter (0.03oz/cf) of di-n-butyl phthalate, 120 mg/l (0.12 oz/cf) of2,4-dinitrophenol, 21 mg/l (0.021 oz/cf) of 2,4-dinitrotoluene and 75mg/l of methyl tert-butyl ether. The mixture was fed to the anoxic tank.

The membrane biological reactor was first operated without granularactivated carbon to obtain a baseline. It was determined that prior tothe addition of granular activated carbon, only about 92% of thebiologically refractory or biologically inhibitory organic chemicaloxygen demand (COD) compounds in the effluent were removed, after a longperiod of bio-acclimation such that the membrane biological reactor wasfully acclimated, thus allowing about 8% of these compounds (measured asCOD) to pass into the effluent).

To determine the efficacy of granular activated carbon, 3800 grams (g)(134 ounces (oz)) MeadWestvaco Nuchar® WV B having nominal mesh sizes of14×35 (based on U.S. Standard Sieve Series) was added to the aerationtank and the blower supplying air to the aeration tank was adjusted tofeed 2124 standard liters per minute (slm) (75 scfm (scfm)) to theaeration tank, with the excess air provided to maintain the granularactivated carbon in suspension. The amount of granular activated carbonadded to the aeration tank was based on 20 percent of the mixed liquorsuspended solids in the unit, which was determined to be approximately5000 mg/l (5 oz/cf).

After acclimation of the MLVSS, the total membrane operating systemeffluent COD concentration was less than 4%, therefore achieving greaterthan 96% removal of biologically refractory or biologically inhibitoryorganic compounds that were measured as COD. FIG. 14 is a chartdepicting feed concentration (in mg/l) of biologically refractory andbiologically inhibitory compounds, and the remaining effluentconcentrations (as percentages of the original), at various stages ofbiological acclimation of a membrane biological reactor system. Inparticular, FIG. 14 shows the comparison between the effluentconcentrations prior to addition of granular activated carbon (stage A),during the acclimation period (stage B), and after acclimation (stageB). Once granular activated carbon was added to the system, there was avery significant initial drop in effluent COD concentration, which isnot shown in FIG. 14 as the adsorption capacity of the granularactivated carbon was exhausted in less than one day. The system thenstabilized such that around 6.5% of the feed COD was remaining aftertreatment. This represented a period in which the adsorptive capacity ofthe carbon was exhausted and the biomass on the granular activatedcarbon started working to digest the biologically inhibitory organiccompounds that were measured as COD. After the bacteria became fullyestablished onto the surface of the granular activated carbon, as wasconfirmed with an electron microscope evaluation, the benefits of anattached growth/fixed film system became apparent. The residual CODconcentration in the effluent dropped to less than 4% of the feed CODconcentration, providing a COD removal efficiency of greater than 96%for a highly concentrated feed of biologically refractory orbiologically inhibitory organic compounds.

Use of the method and apparatus of the invention eliminates the pluggingand abrasion of the membranes by keeping the carbon out of the membraneoperating system tank(s). By using larger sized carbon granules, carbongranule screening and/or separation is possible. On the other hand, thesmall particle size of the powdered activated carbon prevents itseffective filtration from the mixed liquor.

Example 2

Laboratory particle suspension scale tests were performed using a 2000milliliter graduated cylinder having a rotameter connected to a sourceof compressed air and a tube from the outlet of the rotameter to a tubethat reached to the bottom of the graduated cylinder. 20 g (0.7 oz) ofthoroughly dried granular activated carbon were placed in the cylinder.Room temperature distilled water was also added to the cylinder wettingthe particles. The contents of the cylinder were mixed with a spatula tosuspend the entire contents and remove air bubbles.

Air was added to the tube in the cylinder at increasing rates until thefirst solids were suspended and the air flow was recorded. The airflowwas increased until approximately 50% of the solids were suspended(based upon the amount of carbon remaining on the bottom of thecylinder) and the airflow was recorded. Airflow was again increaseduntil all of the granular activated carbon was suspended. The finalairflow was recorded. The results are shown in Table 1.

TABLE 1 Air flow in slm Air flow in slm Air flow in slm (scfm) forminimal (scfm) for 50% (scfm) for 100% suspension, suspension,suspension, per ft² of cross- per ft² of cross- per ft² of cross- Carbonsectional area sectional area sectional area Norit Darco 2.83 (0.10)127.4 (4.5) 254.9 (9.0)  MRX/Coal Norit GAC1240 5.38 (0.19) 135.9 (4.8)254.9 (9.0)  Plus/Bituminous Norit Petrodarco 1.70 (0.06)  85.0 (3.0)169.9 (6.0)   8 × 30 Lignite Calgon Filtrasorg 1.70 (0.06) 135.9 (4.8)220.9 (7.8)  400 Bituminous Westates Aquacarb 2.27 (0.08)  85.0 (3.0)169.9 (6.0)  1240/bituminous Jacobi Aquasorb 1.42 (0.05)  85.0 (3.0)169.9 (6.0)  1000/Bitumnous Res Kem 4.25 (0.15) 240.7 (8.5) 339.8 (12.0)CK1240/coal Mead Westvaco 1.70 (0.06)  51.0 (1.8)  93.4 (3.3)  NucharWVB 14 × 35/Wood Mead Westvaco 1.70 (0.06)  68.0 (2.4)  93.4 (3.3) Aquaguard 12 × 40/Wood

The amount of energy required to suspend the particles increased as moreparticles were suspended. Based upon these results, the air requirementsfor suspending a granulated activated carbon were calculated to be about7,080 to about 8,500 slm per 1,000 liters of reactor volume (about 250to about 300 scfm per 1,000 cubic feet of reactor volume). Incomparison, the industry standard for suspending biological solidswithout granulated activated carbon about 850 slm per 1,000 liters ofreactor volume (30 scfm per 1,000 cubic feet of reactor volume). The airrequirement to suspend the granulated activated carbon and thebiological solids was determined to be up to 10 times greater, using asimple coarse bubble diffuser system, than that to suspend thebiological solids alone and to provide the required oxygen forbiodegradation.

Example 3

A granular activated carbon suspension pilot unit was prepared,utilizing a vertical cylindrical tank having a diameter of 1.83 meters(m) (6 feet (ft)) and a water depth of 2.59 m (8.5 ft). One eductor jetnozzle from Siemens Water Technologies (Rothschild, Wis., USA) wasinstalled through an outer wall of the tank at a distance of 43.5centimeters (cm) (17.125 inches (in)) from the tank floor. The nozzle,shown in FIG. 15, was directed horizontally towards the center of thetank. A 50 mg/l concentration of granular activated carbon, MeadWestvaco Nuchar WVB 14×35/Wood, was introduced into the tank.

As depicted in FIG. 15, the jet nozzle system included a jet nozzle 1544which comprised a fluid inlet 1546, a compressed air inlet 1558 and anoutlet 1564. Fluid passed from inlet 1546 to a mixing chamber 1566.Compressed air also entered mixing chamber 1566 where it expanded andimparted energy to the fluid. As the air expanded, the mixture of fluidand air passed to a nozzle throat 1568 where velocity of the mixtureincreased. The fluid containing air exited nozzle 1544 through outlet1564 into the tank.

Tests were conducted with various liquid flow rates and compressed airflow rates. Liquid flows ranged from 530 liters per minute (lpm) to 757lpm (140 gallons per minute (gpm) to 200 gpm) while compressed air flowrates ranged from 0 to 850 slm (30 scfm)

At a liquid flow rate of 587 lpm (155 gpm), an air flow rate of 850 slm(30 scfm) resulted in suspension of the activated carbon, while airflows of 425 slm (15 scfm) and less resulted in deposition of theactivated carbon on the bottom of the tank. Similarly, at a liquid flowrate of 644 lpm (170 gpm), an air flow rate of 850 slm (30 scfm)resulted in suspension of the activated carbon, while an air flow rateof 425 slm (15 scfm) and less resulted in settling of the activatedcarbon on the bottom of the tank. Increasing the liquid flow to 700 lpm(185 gpm) resulted in suspension of the activated carbon at a reducedair flow rate of 425 slm (15 scfm.).

Increasing the flow rate of the liquid through the nozzle from 644 to700 lpm (170 to 185 gpm), an increase of less than 10%, reduced theconsumption of air by 50% as compared to the air required by a coarsebubble diffuser system. As such, the jet suspension system significantlyreduced the consumption of compressed air, and therefore the energycosts associated with the use of compressed air.

Example 4

Example 4 was conducted to determine the efficacy of jet nozzle toperform suspension of granular activated carbon and to demonstratestructures for minimizing passage of granular activated carbon particlesto the membranes of a downstream membrane operating system. Acylindrical tank and a jet mix nozzle were used to demonstrate that jetmixing could suspend granular activated carbon completely. Variousmixing liquid and gas flow rates were evaluated.

As illustrated in FIGS. 16, 18 and 19, a jet mixing/aeration nozzle 1644was installed in a six foot diameter, 9,085 l (2,400 gal) steel tank1602 filled with about 7,570 l (about 2,000 gal) of filtered tap waterto a level L.

In this example, wood-based Mead Westvaco Nuchar® WV-B granularactivated carbon and coal-based Norit Darco® MRX granular activatedcarbon were suspended utilizing a jet mixing nozzle in a cylindricaltank at various liquid and gas flow rates. The Mead Nuchar® WV-Bgranular activated carbon had a specific gravity of 1.1, an effectivesize of 0.6 millimeters (0.024 in), and is typically relatively softerthan coal-based granular activated carbon; the Darco® MRX had a specificgravity of 1.5 and an effective size of 0.7 millimeters (0.028 in).

Approximately 50 mg/l (0.05 oz/cf) of wood-based granular activatedcarbon was added to the water. The low concentration of granularactivated carbon was used to permit viewing of the mixing profile in thetank using a submersible video camera. Table 2 below shows the range oftest conditions used.

TABLE 2 Test conditions for granular activated carbon jet suspensionCondition Liquid Rate, 1 pm (gpm) Air Rate, slm (scfm) 1 530 (140)  0(0)  2 587 (155) 425 (15) 3 644 (170) 850 (30) 4 700 (185) 425 (15) 5757 (200)  0 (0)  6 644 (170) 425 (15) 7 700 (185)  0 (0)  8 700 (185)850 (30) 9 644 (170)  0 (0)  10 587 (155) 850 (30) 11 587 (155)  0 (0) 

Water was fed to the nozzle of jet mixing/aeration aerator 1644 by discpump 1648 and compressed air was injected from blower 1660. Variablefrequency drives 1649 and 1661 controlled the speed of the pump andblower motors, respectively, allowing adjustment of the respective feedrates. A magnetic flow meter in the discharge line of the disc pump 1648monitored the liquid flow. The speed of the blower motor wasproportional to the air flow.

Referring to FIG. 17, the throat velocity of the jet nozzle wascalculated at each test condition and plotted versus the liquid flowrate. As shown, a minimum throat velocity of approximately 10.4 metersper second (34 feet per second) was required to achieve completesuspension of the wood-based granular activated carbon. This velocitycan be correlated to the specific gravity and maximum particle size ofthe granular activated carbon.

At the completion of the testing with the wood-based granular activatedcarbon, the tank was drained, cleaned and refilled with water andapproximately 50 mg/l of the coal-based granular activated carbon wasadded. Based on a similar series of tests, it was observed that the jetaerator was able to maintain the denser granular activated carbon insuspension.

Since it is necessary to substantially prevent the granular activatedcarbon particles from reaching the membranes of a downstream membraneoperating system, a slotted screen with 0.38 millimeter openings waspositioned at the outlet of the aeration/reactor tank, so that anygranular activated carbon particles that are broken down during the jetaeration circulation to particles having a diameter less than 0.38millimeter (0.015 in) will pass through the screen, allowing them toenter the membrane operating system.

In addition, two tests were performed placing a screen on the suctionside of the jet pump in the aeration/reactor tank using a quiescentzone, i.e., a zone of low turbulence, that would allow the granularactivated carbon to settle before it reached the screen.

In the first test, and referring to FIG. 18, a vertical baffle 1894 wasused to create a near quiescent zone in the aeration tank 1802. Thebaffle extended from 0.61 m (2 ft) above the bottom of the tank to abovethe water level. In this configuration, the screen 1822 was a wedge wirescreen and was mounted near the top of the quiescent zone which requiredwater to be pulled from the bottom of the tank 1802 through the lowturbulence zone before it reached the screen 1822. The quiescent zonewas sized at 40-50% greater than the calculated plug flow of the unit sothat the upward velocity was less than the settling velocity of thegranular activated carbon. For this configuration to be effective, thesettling rate, which is dependent upon the specific gravity of theparticles, must be greater than the upward velocity. The tests wereperformed using the coal-based granular activated for which thecalculated settling rate is 1.8 meters per second. Assuming plug flow inthe quiescent zone, it would need to be at least 0.39 m² (4.2 ft²), tokeep the upward velocity low enough to allow the granular activatedcarbon to settle. The actual cross-sectional area of the zone was 0.73m² (7.8 ft²).

Still referring to FIG. 18, nozzle 1844 of tank 1802 that was used tofeed the pump was located approximately 15.2 cm (6 in) from the tankfloor. Polyvinyl chloride pipe was attached to nozzle 1844 using arubber boot so that a wedge wire screen 1822 could be suspended near thetop of the tank and in fluid communication with the outlet 1808. Thewedge wire screen was 8.9 cm (3.5 in) in diameter, 0.91 m (3 ft) longand had 0.38 millimeter (0.015 in) openings.

The mixing test was conducted with a water flow of 700 lpm (185 gpm) andan air flow of 419 slm (14.8 scfm) for a run time of approximately 18hours. Granular activated carbon was observed on the floor of the tankunder the quiescent zone with less granular activated carbon still insuspension in the turbulent portion of the tank. Occasionally, aswirling action would occur on the floor below the quiescent zone andsome of the granular activated carbon would be carried upwards towardthe screen.

When the pump and blower were turned off, a portion of the granularactivated carbon that was present on the screen fluffed off indicatingit was not strongly adhered to the screen; the remaining granularactivated carbon was easily removed with a light brushing.

Referring to FIG. 19, the second test was conducted using a tank 1902,vertical baffle 1994, nozzle 1944, and screen 1922 in fluidcommunication with an outlet 1902 dimensioned and positionedsubstantially identically to equivalent elements described with respectto FIG. 18. In addition, a second baffle 1993 was positioned at an angleof 45° below the vertical baffle 1994 to dissipate the upward flow. Thequiescent zone provided a means for minimizing the amount of granularactivated carbon that reached the screen. Either a mechanical wiper orback-flushing pulse of water or air can be used to dislodge any granularactivated carbon that may accumulate on the screen over time.

Example 5

Example 5 was conducted to demonstrate the effectiveness of air liftpump systems using draft tube and trough mixing to efficiently suspendthe same wood-based and coal-based granular activated carbon materialsused in Example 4. Cylindrical and rectangular tanks were used invarious configurations. Attrition was measured using both the wood-basedgranular activated carbon and coal-based granular activated carbon ofExample 4; the mixing test used the higher density coal-based granularactivated carbon.

The test data established that granular activated carbon can besuspended in draft tubes and draft troughs in both cylindrical andrectangular tanks using air rates comparable to those required tosustain biological respiration in such tanks. The data also shows thatat a constant air flow rate, a larger diameter draft tube is moreefficient than a smaller draft tube in terms of moving the granularactivated carbon from the surrounding area on the floor of the tank andinto suspension.

In order to determine the extent of granular activated carbon attrition,a 0.31 m (12 in) diameter, 3.7 m (12 foot) high section of acrylic pipewas filled to 2.3 m (92 in) with 150 l (5.3 gal) of water, and 1,500 g(53 oz) of dry granular activated carbon was added to provide aconcentration of approximately one weight percent. A polyvinyl chloridepipe having a diameter of 2.1 m (82 in) long, 7 cm (3 in) was secured inthe center of the 0.31 m (12 in) diameter pipe to serve as the drafttube. Four slots measuring 2.54 cm (1 in) high by 1.9 cm (0.75 in) widewere provided in the bottom of the tubing for passage of the granularactivated carbon and water and a 1.9 cm (0.75 in) in nozzle was placedin the center of the draft tube.

Air was introduced via the nozzle at a rate of 2,831 standard liters perhour (100 standard cubic feet per hour), which was equivalent to about300 slm per 1000 liters of water (300 scfm per 1000 cubic feet ofwater). This relatively high air flow rate was chosen to produce moreturbulent mixing than would be expected in a full-scale operation inorder to determine attrition. The fluid was allowed to mix forapproximately 10 minutes before the first sample was taken.

Attrition was measured during the test by taking grab samples of thewater and granular activated carbon from the top of the acrylic pipe andpouring the sample through a 20 mesh screen. The solids that passedthrough the screen and which were assumed to have resulted fromattrition were collected, dried and weighed.

The results indicated that the granular activated carbon attrition ratewas greater for the wood-based granular activated carbon (WV-B) than thecoal-based granular activated carbon (MRX). After 30 days of operation,approximately 10% attrition of the wood-based granular activated carbonand about 5% attrition of the coal-based granular activated carbon wasobserved. In the practice of the invention in a working bioreactor, thisamount of attrition would be made up through solids wasting duringnormal operation of the biological process. The results from the testingare summarized in FIG. 20. The plot also shows the y-intercept valuesand R² values for standard linear regression analysis for each data set.

Draft tube(s) of various configurations and variables such as the numberof draft tubes, distance of the draft tube from the bottom of the tankand the draft tube diameter were tested and shown to effect performance.

In one configuration, and referring to FIG. 21, a single 0.3 m (12 in)diameter, 1.5 m (5 ft) high draft tube 2192 was placed in the center of1.8 m (6 ft) diameter tank 2102 and positioned above the bottom of thetank on legs 2195. The tank 2102 was filled with approximately 6,435 l(1,700 gal) of water to a water level L and sufficient coal-basedgranular activated carbon (400-1,200 g (14.1-42.3 oz)) added to permitunaided viewing and recording of the mixing characteristics. Air wassupplied by a 2.54 cm (1 in) diameter polyvinyl chloride course bubblediffuser pipe 2190 that passed through the draft tube wall and which hadseveral 3.2 millimeter (0.125 in) diameter holes drilled through its topsurface. The air flow rate was varied from 141 slm (5 scfm) to 425 slm(15 scfm), and the distance D between the bottom of the tank and drafttube was either 8.3 cm (3.25 in) or 1.9 cm (0.75 in).

As used in connection with this series of tests, the term “impact zone”is the area of the tank floor around the draft tube which was free ofgranular activated carbon.

It was observed that with the draft tube positioned 8.3 cm (3.25 in)above the tank floor, the impact zone was larger than when the drafttube was positioned 1.9 cm (0.75 in) above the tank floor, otherconditions being the same. The optimum distance between the bottom ofthe draft tube and the tank floor for prevailing conditions can bedetermined by routine experimentation.

A two-fold increase in the amount of air added did not double the sizeof the impact zone. At 425 slm (15 scfm) with a gap between the floorand draft tube of 8.3 cm (3.25 in), an impact zone of approximately 71cm (28 in) in diameter, i.e., 20 cm (8 in) beyond the outside wall ofthe draft tube, was produced and was the largest impact zone observed.

In an effort to expand the size of the impact zone using the same amountof air, the configuration shown in FIG. 21 was modified by addition of askirt or flange extending horizontally from the bottom of the draft tubewhich increased the overall diameter of the draft tube and skirt to 71cm (28 in). All other conditions were the same as described above. Theair flow rate was varied between 141 slm (5 scfm) and 425 slm (15 scfm).

It was observed that adding a skirt to the bottom of the draft tube didincrease the size of the impact zone. The impact zone was increased to112 cm (44 in), i.e., 20 cm (8 in) beyond the outer edge of the skirt,at an air rate of 425 slm (15 scfm), as compared to an impact zone of 71cm (28 in) with the same air rate without the skirt. The impact zone wasincreased in proportion to the size of the skirt.

These draft tube configurations produced a flow pattern that isillustrated in FIG. 22 in which water and suspended granular activatedcarbon are drawn down and inwardly toward the inlet 2296 of draft tube2290. Stagnant regions are also represented in FIG. 22.

In a further example, a smaller diameter and shorter draft tube waspositioned inside a larger draft tube, both being 1.82 m (6 ft) inlength with the inner draft tube mounted approximately 7.6 cm (3 in)from the bottom of the tank and the outer draft tube positioned 22.9 cm(9 in) higher than the inner draft tube. A polyvinyl chloride sheetextended from the bottom of the 15.3 cm (6 in) inner draft tube tocreate a 71 cm (28 in) diameter skirt. Plastic sheeting was attached tothe top edge of the skirt and at a position approximately 12.7 cm (5 in)up the exterior surface of the 15.3 cm (6 in) diameter draft tube toform an inclined surface, or ramp. The modified draft tube was placed inthe center of the 1.82 m (6 foot) diameter tank; the air rate was variedbetween 141 slm (5 scfm) and 425 slm (15 scfm).

The concentric tube produced an impact zone of approximately 112 cm (44in), which was comparable to that of a single draft tube with a 71 cm(28 in) diameter flange skirt. In both configurations, the impact zonewas approximately 112 cm (44 in).

The draft tube configuration of FIG. 21 was modified by replacing the0.31 m (12 in) diameter draft tube with a single 15.3 cm (6 in) diameterdraft tube. The air flow rate was again varied from 141 slm (5 scfm) and425 slm (15 scfm), and the spacing between the bottom of the tank andthe draft tube was tested at 8.3 cm (3.25 in) and 6.4 cm (2.5 in).

The results of these tests indicated that a variation in the spacingfrom 8.3 cm (3.25 in) and 6.4 cm (2.5 in) did not significantly changethe diameter of the impact zone around the tube.

A two-fold increase in the air flow rate did not double the size of theimpact zone. The condition that produced the largest impact zone was 425slm (15 scfm) with a space of 8.3 cm (3.25 in) between the floor anddraft tube. This configuration created an impact zone that wasapproximately 56 cm (22 in) in diameter, 20 cm (8 in) beyond the outsidewall of the draft tube.

Based on the above tests, it can be concluded that for a given air rate,a larger diameter draft tube is more effective in suspending thegranular activated carbon than a smaller draft tube within the rangesand sizes tested. It appears that more than one draft tube would berequired to mix and suspend the granular activated carbon in a 1.82 m (6foot) diameter tank. Although increasing the air rate did increase therate of mixing and the size of the impact zone up to a point, doublingthe air rate did not double the impact zone. The tank floor in an areaapproximately 20 cm (8 in) beyond the periphery of the draft tube, withor without a skirt or flange, was consistently cleared of granularactivated carbon. Alternative constructions and/or supplemental mixingdevices can be employed in the tank to push the granular activatedcarbon toward the draft tube impact zone(s).

In another configuration, and referring to FIG. 23, three evenly spaced12 in diameter draft tubes 2392 were placed in a tank 2302 and securedto each other so that the center of each draft tube would be 0.61 m (24in) from the center of the tank, with a distance of approximately 0.31 m(12 in) from the center of the draft tubes to the tank wall. Each drafttube was suspended approximately 7 cm (3 in) off the tank floor.

Air was uniformly supplied to each draft tube through 1 in diameterpolyvinyl chloride pipes, each provided with two 3.2 millimeter (0.125in) holes. The total air provided to all three of the draft tubes was453 slm (16 scfm).

In order to supplement the mixing and movement of the granular activatedcarbon outside of the impact zones that formed directly adjacent to thethree draft tubes, a water distribution system of 2.54 cm (1 in)polyvinyl chloride pipe with holes was fabricated for placement in thebottom of the tank. Holes were drilled approximately 32 cm (7 in) aparton alternating sides of the pipe so that the water would be directedtowards the floor at a 45° angle. Water was supplied to the distributionsystem at 53 lpm (14 gpm) by a centrifugal pump from a separate waterstorage and recycling tank. This arrangement is analogous to the returnwater from the membrane operating system tank in a membrane bioreactorsystem. A second pump and valve controlled the flow of water back to thestorage tank and a screen was used to retain granular activated carbonin the test tank.

It was observed that each draft tube cleared an area extending 20 cm (8in) beyond the outside wall of the draft tube and that each hole in thewater distributor system cleared an area 31-41 cm (12-16 in) long and20-31 cm (8-12 in) wide. In the areas in between the impact zones of thedraft tubes and water distributors, some granular activated carbonsettled to the tank floor, but did slowly move into the impact zoneswhere it was lifted into suspension.

In a further test of the water distribution system, the holes in thewater distributor pipes were oriented to cause the water discharged tomix the tank in a circular pattern.

All other conditions including the spacing of the water distributorpiping, air flow rate and water flow rate were the same as described inconnection with the three 31 cm (12 in) diameter 91 cm (36 in) highdraft tube in which membrane operating system return water was addeduniformly to the tank.

The results from this test indicated that each draft tube cleared anarea extending 20 cm (8 in) beyond the outside wall of the draft tube.Additionally, the water flow was effective at mixing the granularactivated carbon in a circular pattern. The build up of granularactivated carbon in the center of the tank can be eliminated by placingone draft tube in the center of the tank instead of three draft tubesaround the perimeter.

It was observed that granular activated carbon was mixed to the top ofthe water level in the tank even when the length of the draft tubes wasreduced from 152 cm (60 in) to 91 cm (36 in). Additionally, using waterdistributors to add return liquid to the bottom of the tank waseffective to move the granular activated carbon around. When multipledraft tubes were placed inside of the tank, the size of the impact zonearound each draft tube was equivalent to the size of the impact zoneobserved around a single draft tube, i.e., 20 cm (8 in) beyond the outerwall of the draft tube.

In another configuration, and referring to FIG. 24, and for comparisonof the mixing characteristics with those of the circular tank, arectangular tank 2402 was provided that was 0.91 m (3 ft) wide, 2.1 m (7ft) long and 2.7 m (9 ft) deep, and was filled with 2.4 m (8 ft) ofwater. The blower, blower motor, and flow meter was set up and operatedas discussed above.

As shown in FIG. 24, the outside 31 cm (12 in) of the tank floor 2405was sloped at an angle of 30°, which had previously been determined tobe the angle at which the granular activated carbon commenced to slidein an aqueous environment. The 30° angle of the sloping wall caused thegranular activated carbon to be directed towards the draft tube inlets.

Three 31 cm (12 in) diameter draft tubes 2492, each 91 cm (36 in) highand supported approximately 12.7 cm (5 in) off of the bottom of thetank, were evenly spaced across the non-sloped portion of the tank 2402.A 7.6 cm (3 in) diameter air pipe 2490 having drilled openings waspositioned below the draft tubes for introduction of air into the drafttubes via three coarse bubble diffusers. The air flow rate was variedfrom 221 slm (7.8 scfm) to 512 slm (18.1 scfm).

The granular activated carbon was satisfactorily mixed at all of the airrates employed in the range. The higher the air rate, the more vigorousthe mixing flow, and the less time the granular activated carbonremained on the floor of the tank. During air addition, granularactivated carbon was observed to be present throughout all depths of thetank.

In another configuration, and with reference now to FIG. 25, a tank 2502was provided having sloping walls and diffuser described above inconnection with FIG. 24, with the addition of two parallel baffles 2597that were 61 cm (24 in) high, spaced 31 cm (12 in) apart and positioned6.4 cm (2.5 in) above the tank floor to form a “draft trough” 2592. Theair flow rate through pipe 2590 was varied from 90.6 slm (3.2 scfm) to331.3 slm (11.7 scfm). It was observed that the granular activatedcarbon was mixed and suspended well at all air rates greater than 141.6slm (5 scfm), and increasing the air rate to above 141.6 slm (5 scfm)increased the rate of mixing.

In a further test in which the tank floor and diffuser configurationswere identical to the tests described with respect to FIGS. 24 and 25,without a draft trough or draft tubes, it was found that at even 1133slm (40 scfm), there was visibly less than 10% of the granular activatedcarbon in suspension, indicating that the presence of the trough is avery significant factor in the energy-efficient suspension of thegranular activated carbon.

In another test configuration, the distance from the tank walls to thetrough was increased. In a large aeration basin, it would beeconomically beneficial to be able to space the troughs apart at greaterdistances. A test was performed to determine the efficacy of extendingthe spacing between troughs to 2.1 m (7 ft). To determine this, theconfiguration described above and with respect to FIG. 25 was rotated90° in the tank. Two 30° sloping walls were installed that extended 91cm (36 in) from each end of the tank.

A coarse bubble diffuser was fabricated by drilling nine 3.2 millimeter(0.125 in) diameter holes evenly spaced along the 91 cm (36 in) of a 7.6cm (3 in) diameter polyvinyl chloride pipe. The air flow rate was variedfrom 164 slm (5.8 scfm) to 402 slm (14.2 scfm).

The bubble diffuser was placed in the center of the tank. A trough wascreated between the two sloping tank walls around the diffuser pipeusing two parallel baffles that were 91 cm (36 in) long, 61 cm (24 in)high, spaced 31 cm (12 in) apart and 6.4 cm (2.5 in) above the tankfloor.

It was observed that the granular activated carbon was mixed andsuspended well over the entire air rate range. The granular activatedcarbon was swept down the slope and into the draft trough whichindicated that the spacing of the troughs could be up to 2.1 m (7 ft)apart with a 30° sloped floor between them.

Testing as described above indicated that the draft trough design wassuccessful at suspending the granular activated carbon in the 0.91 m (3foot) wide, 2.1 m (7 foot) long by 2.4 m (8 foot) volume of water usinga 30° sloped floor or wall that extended from the vertical outside wallstoward the draft trough.

Additional tests were performed using a 91 cm (36 in) long trough asdescribed above with different configurations of the tank floor tofurther optimize the energy-efficient performance to suspend thegranular activated carbon. The configurations included removing thesloped floor entirely, sloping the floor from the outside wall to thetrough and reducing the angle from 30° to 15°, and decreasing the lengthof the sloped floor from 91 cm (36 in) on each end of the tank to 31 cm(12 in) on each end while maintaining the 30° angle. In addition, a testwas performed in which the tank was configured with two 91 cm (36 in)long troughs at each end of the tank without a sloped floor. In each ofthese configurations the air flow rate was varied between 141 slm (5scfm) to 425 slm (15 scfm).

Two draft troughs were installed on each end of a pilot aeration tank.The troughs were created by placing a 91 cm (36 in) coarse bubblediffuser at each end of the tank. The diffuser was fabricated from 7.6cm (3 in) polyvinyl chloride pipe having 5 evenly spaced 3.2 millimeter(0.125 in) holes. Approximately 20 cm (8 in) away from the wall, i.e., 6in from the center of the diffuser, a 91 cm (36 in) long and 61 cm (24in) high baffle plate was mounted approximately 5.1 cm (2 in) off thetank floor.

From the testing that was performed in the rectangular pilot scaleaeration tank, it was observed that adding three 31 cm (12 in) diameter,91 cm (36 in) high draft tubes over the diffuser suspended the granularactivated carbon at air rates between 227 slm (8 scfm) and 510 slm (18scfm). However, this configuration could result in the formation ofstagnant zones near the supports and in the corners of the tank. Placinga 2.1 m (7 foot) long draft trough in the center of the tank and slopingthe floors at a 30° angle produced thoroughly mixing and suspension ofgranular activated carbon in the tank at air rates above 141 slm (5scfm). Further testing indicated that adequate mixing can be obtainedwith the draft troughs spaced up to 2.1 m (7 ft) apart.

In the above-described configurations using draft tubes, there appearedto be a diminishing return from increasing the air rate. Increasing theair rate did increase the rate of mixing and the size of the impactzone. However, doubling the air rate did not double the impact zone. Theimpact zone for each draft tube appeared to extend approximately 20 cm(8 in) beyond the outside edge of the tube. Beyond this region,supplemental local mixing of the material in the tank was required tomove the granular activated carbon on the tank floor toward and into thedraft tube impact zone. A water distribution system was used toaccomplish this mixing.

Granular activated carbon was suspended at all depths of the tank evenwhen the length of the draft tube was reduced from 152 cm (60 in) to 91cm (36 in). Sloping the floor of the tank at a 30° angle towards thedraft tubes or troughs provides an effective method of circulating thegranular activated carbon. The use of draft troughs and a sloped floorprovided complete mixing of the granular activated carbon in therectangular shaped tank and was less susceptible to formation ofstagnant zones than using draft tubes. The draft trough was effective atlifting granular activated carbon off of the tank floor. Once thegranular activated carbon was lifted above the trough, the mixingcreated by the coarse bubble diffusers was sufficient to lift thegranular activated carbon to the top of the tank. Test results indicatedthat utilizing a 30° sloped surface allowed the center of the troughs tobe spaced 2.1 m (7 ft) apart, and greater spacing may be possible.

Example 6

A wastewater treatment system designed substantially in accordance withone or more embodiments of the invention described above and illustratedin the figures comprises a first biological reactor, and a secondbiological reactor that includes granular activated carbon positioneddownstream of the first biological reactor. A membrane operating systemis positioned downstream of the biological reactors. Operationalparameters such as flow rates, residence times, temperature, pH levels,and amount of granular activated carbon present in the system areadjusted to identify conditions for optimum performance, and provideacceptable levels of biological oxygen demand and chemical oxygen demandcompounds exiting the system in the effluent. The hydraulic flow betweenthe first reactor and the second reactor is controlled to provide a flowin the downstream direction and to maintain the granular activatedcarbon in the second reactor.

During operation, a wastewater stream is introduced into the firstbiological reactor. Phosphorus, nitrogen, and/or pH adjustment materialsare added as needed to maintain optimal nutrient ratios and pH levels inthe first reactor. The micro-organisms in the first reactor are capableof breaking down at least a portion of the biologically labile organicsin the wastewater and reduce the biological oxygen demand compounds inthe effluent to an acceptable level. The second biological reactor whichcontains the granular activated carbon is used to treat the biologicallyrefractory and bio-inhibitory compounds in the wastewater and reducesthe chemical oxygen demand compounds in the effluent to an acceptablelevel.

The granular activated carbon is maintained in suspension in the secondreactor using a suspension system. A screen is positioned in the secondreactor to maintain the membrane operating system substantially free ofgranular activated carbon. The granular activated carbon is added to thesecond reactor as needed, based on biological oxygen demand and chemicaloxygen demand compounds measured in the effluent.

Effluent from the second reactor is introduced to the membrane operatingsystem after passing through the screen. In the membrane operatingsystem, the treated wastewater will pass through one or more membranes.The membrane permeate will be discharged through an outlet of themembrane operating system. The retentate, including activated sludge,will be returned to the first reactor through a return activated sludgeline.

Spent granular activated carbon from the second biological reactor isremoved periodically through a mixed liquor waste discharge port. Awaste outlet is also connected to the return activated sludge line todivert some or all of the return activated sludge for disposal, forinstance, to control the concentration of components in the reactor.

The system includes a controller to monitor and adjust the system asdesired. The controller directs any of the parameters within the systemdepending upon the desired operating conditions and desired quality ofthe effluent streams. The controller adjusts or regulates valves,feeders or pumps associated with each potential flow, based upon one ormore signals generated by sensors or timers positioned within thesystem, or based upon an upward or downward trend in a characteristic orproperty of the system monitored over a predetermined period of time.The sensor generates a signal that can indicate that the concentrationof pollutants such as biologically refractory/inhibitory organic andinorganic compounds has reached a predetermined value or trend, whichtriggers the controller to initiate a corresponding predetermined actionupstream from, downstream from, or at the sensor. This action caninclude any one or more of adding granular activated carbon to thebiological reactor, adding a different type of adsorbent material,adjusting flow of the wastewater to a reactor within the system,redirecting flow of the wastewater to a storage tank within the system,adjusting air flow within a biological reactor, adjusting residence timewithin a biological reactor, and adjusting temperature and/or pH withina biological reactor.

In order to achieve the predetermined levels of biological oxygen demandand chemical oxygen demand compounds in the effluent, the first andsecond reactors are operated with their own hydraulic residence times.The hydraulic residence time of the first and second reactors are variedto determine the optimum ratio of first reactor hydraulic residence timeto second reactor hydraulic residence time. The total hydraulicresidence time of the system should be equal to, or less than a standardsingle biological reactor, e.g., between about 8 and 12 hours. In apreferred mode of operation, the first reactor will have a hydraulicresidence time of between about 4 hours and about 8 hours, while thesecond reactor will have a hydraulic residence time of about 4 hours.Generally the hydraulic residence time of the first reactor will belonger than the hydraulic residence time of the second reactor; however,the relative times will vary depending on the type of wastewater beingtreated. The hydraulic residence time and the flow rates of the systemare used to determine the size of each reactor in accordance withstandard practices in the art. The effluent from the system should belower in chemical oxygen demand compounds by at least about 10% whencompared with the effluent from a standard single biological reactor.Additionally, in a preferred embodiment, the regeneration of thegranular activated carbon is accomplished through use of this system.

Example 7

A bench scale system to simulate activated sludge treatment followed bya combined activated sludge/granular activated carbon treatment wasconstructed and tested. This test was performed to determine theeffectiveness of using granular activated carbon in a biological reactor(the second stage reactor) downstream of a biological reactor withoutgranular activated carbon (first stage reactor).

The first stage reactor was a 4 liter (1.06 gal) tank that containedonly activated sludge. A fine bubble air diffuser was used having an airflow rate of 370 cm³/min (23 in³/min). The second stage reactor was a 3liter (0.79 gal) tank that contained activated sludge and a coal basedgranular activated carbon (AquaCarb® Carbon of Siemens WaterTechnologies Corp.). The granular activated carbon had a U.S. standardmesh size of 8×30. The concentration of granular activated carbon in thesecond stage reactor was 20 g/l (20 oz/cf). A draft tube comprising 5.1cm (2 inches) diameter PVC piping was set up in the second stage reactorhaving a diameter of 12.7 cm (5 inches) to maintain the granularactivated carbon in suspension with an air flow rate of 368 slm (13scfm). The mixed liquor suspended solids concentration in the firststage reactor was about 3,470 mg/l (3.5 oz/cf) while the concentrationin the second stage reactor was about 16,300 mg/l (16.3 oz/cf). Thehydraulic retention time of the first stage reactor was about 6 hoursand the hydraulic retention time of the second stage reactor was about 8hours for a total system hydraulic time of about 14 hours.

The system was operated for over 30 days. The average feed concentrationof soluble COD entering the first stage reactor was 130 mg/l (0.13oz/cf) and the average soluble COD concentration of the effluent of thefirst stage reactor was 70 mg/l (0.07 oz/cf) and was the feed for thesecond stage reactor. The average soluble COD concentration measured inthe effluent of the second stage reactor was 62 mg/l ((0.062 oz/cf).This greater than 10% reduction in soluble COD by the second stagereactor demonstrates the utility of processing wastewater in a systemhaving a biological reactor containing granular activated carbondownstream of a first biological reactor without granular activatedcarbon.

Other aspects of the invention described herein, including a separationsubsystem in the second stage reactor and use of a membrane operatingsystem downstream of the second stage reactor, are applicable to theapparatus described in this example to achieve effective treatment ofwastewater.

The method and apparatus of the present invention have been describedabove and in the attached drawings; however, modifications will beapparent to those of ordinary skill in the art and the scope ofprotection for the invention is to be defined by the claims that follow.

1. A wastewater treatment system comprising: a biological reactorcomprising a separation subsystem constructed and arranged to maintainadsorbent material in the biological reactor with a mixed liquor; asuspension system positioned in the biological reactor, the suspensionsystem constructed and arranged to maintain adsorbent material insuspension with the mixed liquor; and a membrane operating systemlocated downstream of the biological reactor that is constructed andarranged to receive treated mixed liquor from the biological reactor anddischarge a membrane permeate.
 2. The wastewater treatment system ofclaim 1, wherein the suspension system comprises a gas lift suspensionsystem.
 3. The wastewater treatment system of claim 2, wherein the gaslift suspension system comprises at least one draft tube positioned inthe biological reactor and a gas conduit having one or more aperturespositioned and dimensioned to direct gas to an inlet end of the drafttube.
 4. The wastewater treatment system of claim 2, wherein the gaslift suspension system comprises at least one draft trough positioned inthe biological reactor and a gas conduit having one or more aperturespositioned and dimensioned to direct gas to a lower portion of the drafttrough.
 5. The wastewater treatment system of claim 4, wherein the drafttrough is formed by a pair of baffles positioned in the biologicalreactor.
 6. The wastewater treatment system of claim 1, wherein thesuspension system comprises a jet suspension system.
 7. The wastewatertreatment system of claim 1, wherein the separation subsystem includes ascreen positioned at an outlet of the biological reactor.
 8. Thewastewater treatment system of claim 1, wherein the separation subsystemincludes a settling zone located proximate the outlet of the biologicalreactor.
 9. The wastewater treatment system of claim 8, wherein thesettling zone comprises a first baffle and a second baffle positionedand dimensioned to define a quiescent zone in which the adsorbentmaterial separates from mixed liquor and settles into the mixed liquorin a lower portion of the biological reactor.
 10. The wastewatertreatment system of claim 8, further comprising a screen positionedproximate the outlet of the biological reactor.
 11. The wastewatertreatment system of claim 8, further comprising a weir positionedproximate the outlet of the biological reactor.
 12. The wastewatertreatment system of claim 1, further comprising: an adsorbent materialintroduction apparatus in communication with the biological reactor; asensor constructed and arranged to measure a parameter of the system;and a controller in electronic communication with the sensor programmedto instruct performance of an act based on the measured parameter of thesystem.
 13. The wastewater treatment system of claim 12, wherein themeasured parameter is the concentration of one or more predeterminedcompounds.
 14. The wastewater treatment system of claim 12, wherein theact comprises removing at least a portion of the adsorbent material fromthe biological reactor.
 15. The wastewater treatment system of claim 12,wherein the act comprises adding adsorbent material to the biologicalreactor.
 16. A wastewater treatment system comprising: a biologicalreactor with a wastewater inlet, a mixed liquor outlet, and a separationsubsystem associated with the mixed liquor outlet; a suspension systemfor adsorbent material positioned in the biological reactor; a membraneoperating system located downstream of the biological reactor having aninlet in fluid communication with the mixed liquor outlet, and a treatedeffluent outlet.
 17. The wastewater treatment system of claim 16,wherein the suspension system comprises a gas lift suspension system.18. The wastewater treatment system of claim 16, wherein the suspensionsystem comprises a jet suspension system.
 19. A process for treatingwastewater comprising: introducing mixed liquor into a biologicalreactor; introducing adsorbent material into the biological reactor withthe mixed liquor; suspending the adsorbent material in the mixed liquorusing a gas, under operating conditions that promote adsorption ofcontaminants from the mixed liquor by the adsorbent material; andpassing an effluent that is substantially free of adsorbent materialfrom the biological reactor to a membrane operating system whilemaintaining adsorbent material in the biological reactor.
 20. Theprocess of claim 19, wherein liquid is circulated in the biologicalreactor to promote the suspension of the adsorbent material.